For this assignment, click on the link below to go to a website showing Mr. Schuetz getting an automatic speeding ticket in DC.
Your assignment is to use the information provided in the links to find Mr. Schuetz's speed to within 2 miles/hr. You must include the technique, the measurements, and the calculations.
http://www.yhspatriot.net/~aschuetz/subjects/kinematics/aztek_ticket/Schuetz_speeding.htm
Monday, December 04, 2006
Sunday, December 03, 2006
done with electricity, now on to motion!
Now that we are finished with the unit on electricity and magnetism, we are embarking on the study of motion (called kinematics) that will take us through to the spring.
This study will include lots of topics, including speed, acceleration, force, gravity, momentum, and more.
Many of the labs will include measuring time and distance, whether by hand or by computer assisted means.
We will emphasize the importance of measuring technique, calculation, and error analysis.
Our first few assignments:
Measure Hunt: Both in the classroom and at home, we are examining measurement and units.
Accuracy and Precision: Using a bullseye target we are looking at how data could be collected well or poorly, how the term "human error" is really a worthless thing for us to talk about.
When we discuss sources of error, we really only want to talk about the specific ways that our data was skewed. Is it random (some high, some low) or systematic (all high)?
We then move on to the bowling ball lab, our first lab to measure motion and start talking about "inertia" and "speed"
This study will include lots of topics, including speed, acceleration, force, gravity, momentum, and more.
Many of the labs will include measuring time and distance, whether by hand or by computer assisted means.
We will emphasize the importance of measuring technique, calculation, and error analysis.
Our first few assignments:
Measure Hunt: Both in the classroom and at home, we are examining measurement and units.
Accuracy and Precision: Using a bullseye target we are looking at how data could be collected well or poorly, how the term "human error" is really a worthless thing for us to talk about.
When we discuss sources of error, we really only want to talk about the specific ways that our data was skewed. Is it random (some high, some low) or systematic (all high)?
We then move on to the bowling ball lab, our first lab to measure motion and start talking about "inertia" and "speed"
Thursday, November 16, 2006
Electromagnetic
The modern era is based not just on electricity, but the relationship between electricity and magnetism, and the fact that electricity can create a magnetic field which causes repulsion/attraction to other magnetic fields. This creates mechanical motion.
The electric motor.
Run backwards, mechanical motion can generate electricity. By a process called induction, a magnet moving relative to a coil of wires will induce a current in the wire.
We talked for about 45 minutes on Block day about these connections/relationships, and now on Friday we will be in the computer lab doing some further investigations of the phenomena.
This includes using Crocodile Physics (see link from a week or two ago to download it) as well as simulations and visualizations online.
The following links are from the worksheet that we are working on in the computer lab.
Induction
http://micro.magnet.fsu.edu/electromag/java/faraday2/index.html
http://micro.magnet.fsu.edu/electromag/java/lenzlaw/index.html
The electric motor.
Run backwards, mechanical motion can generate electricity. By a process called induction, a magnet moving relative to a coil of wires will induce a current in the wire.
We talked for about 45 minutes on Block day about these connections/relationships, and now on Friday we will be in the computer lab doing some further investigations of the phenomena.
This includes using Crocodile Physics (see link from a week or two ago to download it) as well as simulations and visualizations online.
The following links are from the worksheet that we are working on in the computer lab.
Induction
http://micro.magnet.fsu.edu/electromag/java/faraday2/index.html
http://micro.magnet.fsu.edu/electromag/java/lenzlaw/index.html
Alternating Current, generators, motors
Electric motor:
http://www.phys.unsw.edu.au/~jw/HSCmotors.html#ACmotors (3 animations)
http://www.walter-fendt.de/ph11e/electricmotor.htm
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/motdc.html
http://electronics.howstuffworks.com/motor1.htm
AC generator:
http://micro.magnet.fsu.edu/electromag/java/generator/ac.html
http://www.walter-fendt.de/ph11e/generator_e.htm
faraday’s experiment:
http://micro.magnet.fsu.edu/electromag/java/faraday/index.html
transformers:
http://micro.magnet.fsu.edu/electromag/java/transformer/index.html
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/transf.html#c1
http://www.phys.unsw.edu.au/~jw/HSCmotors.html#ACmotors (3 animations)
http://www.walter-fendt.de/ph11e/electricmotor.htm
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/motdc.html
http://electronics.howstuffworks.com/motor1.htm
AC generator:
http://micro.magnet.fsu.edu/electromag/java/generator/ac.html
http://www.walter-fendt.de/ph11e/generator_e.htm
faraday’s experiment:
http://micro.magnet.fsu.edu/electromag/java/faraday/index.html
transformers:
http://micro.magnet.fsu.edu/electromag/java/transformer/index.html
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/transf.html#c1
TESLA
Learn more about Nikola Tesla from the PBS website where the documentary was produced.Including some of his inventions: http://www.pbs.org/tesla/ins/index.html
And more about his life/legacy. This section is nicely divided into the same "sections" as the video: http://www.pbs.org/tesla/ll/index.html
On Block day (Wed/Thurs) we watched about half the video.
We will finish it next week.
Wednesday, November 08, 2006
A few solutions to the homework
First, lets start with the last one...
Similar to the one I worked out in the discussion on the previous post.
Total resistance: 10+ 3.333 = 13.333 ohms. This is because the three 10's in parallel give you an equivalent resistance of 10/3.
So, with the voltage of the circuit as 3V, and the resistance is 13.333 ohms, then the current is V/R = I = 3/13.333 = .225 amps.
That's the current through the first resistor, so V=IR gives us V=.225 * 10 = 2.25 Volts.
The current through the other resistors is same .225 amps, split three ways. So .225/3 = .075 amps.
The voltage drop across the other three is 3-2.25 = .75 V (the first resistor had a drop of 2.25, so only .75 was left for the rest. in parallel, each resistor gets the full voltage, so V=0.75 Volts.
The power output of the first resistor is P=IV = .225 * 2.25 = .506 watts
For each of the other three resistors, P=IV=.075 * .75 = .056 watts. So the total power output of the system is P=.506 + .056 + .056 + .056 = .675 watts
Now for the modern holiday lights.
each string of 5 lights has a total of 120V across them.
So the voltage drop across a single bulb is 120/5 = 24 V
if P=2.4W, then P=IV becomes 2.4=I*24, so I=0.1 amps
Since we have 10 of these in parallel, that's a total of 1 amp of current running out of the outlet.
The resistance for a single bulb can be found from V=IR, where V=24 for a single bulb, I=0.1 A running through a single bulb, and so R=V/I = 24/0.1 = 240 ohms.
Yes, this is a very different resistance from the old fashioned bulb.
If one burns out? Well, that set of 5 goes out, but the other 45 lights stay lit.
Most modern bulbs nowadays actually has an extra metal wire that is an even worse conductor than the filament, but is not easily broken, running across the posts inside each little bulb. If the filament breaks, then electricity goes through that other wire and the rest of the lights in the series still gets current.
Read through the older posts on the blog for helpful stuff on the rest of the homework and the quiz.
Good luck with the quiz tomorrow. :-)
Similar to the one I worked out in the discussion on the previous post.
Total resistance: 10+ 3.333 = 13.333 ohms. This is because the three 10's in parallel give you an equivalent resistance of 10/3.
So, with the voltage of the circuit as 3V, and the resistance is 13.333 ohms, then the current is V/R = I = 3/13.333 = .225 amps.
That's the current through the first resistor, so V=IR gives us V=.225 * 10 = 2.25 Volts.
The current through the other resistors is same .225 amps, split three ways. So .225/3 = .075 amps.
The voltage drop across the other three is 3-2.25 = .75 V (the first resistor had a drop of 2.25, so only .75 was left for the rest. in parallel, each resistor gets the full voltage, so V=0.75 Volts.
The power output of the first resistor is P=IV = .225 * 2.25 = .506 watts
For each of the other three resistors, P=IV=.075 * .75 = .056 watts. So the total power output of the system is P=.506 + .056 + .056 + .056 = .675 watts
Now for the modern holiday lights.
each string of 5 lights has a total of 120V across them.
So the voltage drop across a single bulb is 120/5 = 24 V
if P=2.4W, then P=IV becomes 2.4=I*24, so I=0.1 amps
Since we have 10 of these in parallel, that's a total of 1 amp of current running out of the outlet.
The resistance for a single bulb can be found from V=IR, where V=24 for a single bulb, I=0.1 A running through a single bulb, and so R=V/I = 24/0.1 = 240 ohms.
Yes, this is a very different resistance from the old fashioned bulb.
If one burns out? Well, that set of 5 goes out, but the other 45 lights stay lit.
Most modern bulbs nowadays actually has an extra metal wire that is an even worse conductor than the filament, but is not easily broken, running across the posts inside each little bulb. If the filament breaks, then electricity goes through that other wire and the rest of the lights in the series still gets current.
Read through the older posts on the blog for helpful stuff on the rest of the homework and the quiz.
Good luck with the quiz tomorrow. :-)
series and parallel circuits
The last several labs for the quarter involve series and parallel circuits.
While we did an asisgnment on Crocodile Physics where we examined resistors and found the patterns and equations for equivalent resistances, we expanded that in the lab the last few days by looking at how the current and voltage were distributed around a circuit.
The basic logic is this:
1) in a series circuit, the current is the same throughout the series.
2) in a parallel circuit, each bulb is connected independently to the battery, so the voltage drop is the same across each bulb.
More details:
1) in a series circuit, the current that comes out of the battery must go into the first bulb, then out and then into the next and then out, and then into the next and then out... etc. Since the current doesn't "fade" or "get used up", that means that the current is the same value through each resistor in the series circuit.
The voltage, however, drops across each bulb so that the total voltage change should equal the voltage imposed on the circuit by the power supply.
The amount of voltage change for each bulb depends upon how much resistance the bulb has (V=IR). The more resistance, the more "oomph" that goes into going through. This helps us figure out the power, too. P=IV. The total energy that is used up in "pushing" charges through the resistor is the amount of heat energy that causes the bulb to light up. Thus, the brighter the bulb, the more power.
2) in a parallel circuit, the current comes out of the battery and splits up. some goes one way, some goes the other. Since each bulb is connected directly to the battery, the voltage change across each bulb is the total voltage change that the battery imposes. No sharing.
In other words...
in a series circuit, voltages add up and current is constant
in a parallel circuit, voltages are the same, and current adds up.
So... what about that dang combination circuit?
Well, you can first of all consider it as two "things" in series. The first is a single resistor. The second "thing" is a pair of resistors in parallel. So, if they are all identical bulbs, then the second "thing" has a resistance that is half that of the first bulb. That means that more energy is being used up pushing lots of charges through that first bulb. That's the one that will glow brightly. Then by the time you get to the two in parallel, the charges can split up and go both ways, so it is pretty easy going. Half the current goes through each, so they barely will light up, if at all.
Let's do a sample problem of the combination circuit. It won't help a lot to just read this. You have to try to figure it out and be able to do these calculations on your own...
This circuit is a single resistor connected to a pair of resistors in parallel. Like we've seen in class several times already.
All resistors with a resistance of 6 ohms, hooked up to a 4V battery.
The total resistance of the circuit is 6 + 3 = 9 ohms, since the two in parallel combine to make 3.
Using V=IR, we have 4=I*9, so I=4/9 = 0.44 amps. That is the current leaving the battery and entering the whole circuit.
So, that's the current entering the first resistor.
The first resistor remember has a resistance of R=6 ohms, and with a current of I=0.444 Amps, then we know that the Voltage change is V=IR = 0.444*6 = 2.66 V
So, then we know that the voltage change across the parallel chunk of the circuit must be whatever is leftover.
V= 4 V - 2.66 V = 1.33 Volts. So 1.33 Volts is the difference across each of the two resistors in parallel.
Since each resistor in the parallel chunk has a resistance of 6 ohms, and a voltage change of 1.33 Volts, then we know, from V=IR, that the current through each resistor must be
I=V/R=1.33/6 = .22 Amps.
But of course we knew this already, since the total current through the circuit is .44 amps, and the since the resistors are the same, the current should split evenly.
The power output of each bulb is:
#1 P=IV = 0.44 amps * 2.66 Volts = 1.17 Watts
#2 P=IV = 0.22 amps * 1.33 Volts = .293 Watts
#3 P=IV = 0.22 amps * 1.33 Volts = .293 Watts
Notice that the single bulb gets 4 times the energy every second. So it is very bright, the others are very not bright. Half the current AND half the voltage makes it pretty dim.
While we did an asisgnment on Crocodile Physics where we examined resistors and found the patterns and equations for equivalent resistances, we expanded that in the lab the last few days by looking at how the current and voltage were distributed around a circuit.
The basic logic is this:
1) in a series circuit, the current is the same throughout the series.
2) in a parallel circuit, each bulb is connected independently to the battery, so the voltage drop is the same across each bulb.
More details:
1) in a series circuit, the current that comes out of the battery must go into the first bulb, then out and then into the next and then out, and then into the next and then out... etc. Since the current doesn't "fade" or "get used up", that means that the current is the same value through each resistor in the series circuit.
The voltage, however, drops across each bulb so that the total voltage change should equal the voltage imposed on the circuit by the power supply.
The amount of voltage change for each bulb depends upon how much resistance the bulb has (V=IR). The more resistance, the more "oomph" that goes into going through. This helps us figure out the power, too. P=IV. The total energy that is used up in "pushing" charges through the resistor is the amount of heat energy that causes the bulb to light up. Thus, the brighter the bulb, the more power.
2) in a parallel circuit, the current comes out of the battery and splits up. some goes one way, some goes the other. Since each bulb is connected directly to the battery, the voltage change across each bulb is the total voltage change that the battery imposes. No sharing.
In other words...
in a series circuit, voltages add up and current is constant
in a parallel circuit, voltages are the same, and current adds up.
So... what about that dang combination circuit?
Well, you can first of all consider it as two "things" in series. The first is a single resistor. The second "thing" is a pair of resistors in parallel. So, if they are all identical bulbs, then the second "thing" has a resistance that is half that of the first bulb. That means that more energy is being used up pushing lots of charges through that first bulb. That's the one that will glow brightly. Then by the time you get to the two in parallel, the charges can split up and go both ways, so it is pretty easy going. Half the current goes through each, so they barely will light up, if at all.
Let's do a sample problem of the combination circuit. It won't help a lot to just read this. You have to try to figure it out and be able to do these calculations on your own...
This circuit is a single resistor connected to a pair of resistors in parallel. Like we've seen in class several times already.
All resistors with a resistance of 6 ohms, hooked up to a 4V battery.
The total resistance of the circuit is 6 + 3 = 9 ohms, since the two in parallel combine to make 3.
Using V=IR, we have 4=I*9, so I=4/9 = 0.44 amps. That is the current leaving the battery and entering the whole circuit.
So, that's the current entering the first resistor.
The first resistor remember has a resistance of R=6 ohms, and with a current of I=0.444 Amps, then we know that the Voltage change is V=IR = 0.444*6 = 2.66 V
So, then we know that the voltage change across the parallel chunk of the circuit must be whatever is leftover.
V= 4 V - 2.66 V = 1.33 Volts. So 1.33 Volts is the difference across each of the two resistors in parallel.
Since each resistor in the parallel chunk has a resistance of 6 ohms, and a voltage change of 1.33 Volts, then we know, from V=IR, that the current through each resistor must be
I=V/R=1.33/6 = .22 Amps.
But of course we knew this already, since the total current through the circuit is .44 amps, and the since the resistors are the same, the current should split evenly.
The power output of each bulb is:
#1 P=IV = 0.44 amps * 2.66 Volts = 1.17 Watts
#2 P=IV = 0.22 amps * 1.33 Volts = .293 Watts
#3 P=IV = 0.22 amps * 1.33 Volts = .293 Watts
Notice that the single bulb gets 4 times the energy every second. So it is very bright, the others are very not bright. Half the current AND half the voltage makes it pretty dim.
Thursday, November 02, 2006
CROC
Download and run the software to work from home:
http://www.yhspatriot.net/~aschuetz/large_files/Croczip.zip
http://www.yhspatriot.net/~aschuetz/large_files/Croczip.zip
Thursday, October 26, 2006
Lab 7, sample answers
As you are working through lab #7, either in the lab or in Croc physics, you should pay attention to WHAT you are measuring and seeing.
Here are some sample measurements that you probably won't get, but if you look through here you should be able to understand the way that the voltage drops across the circuit and the current works its way through the circuit.
The brightness of a given bulb can essentially be measured in Watts (power usage), which you can find by multiplying the Voltage across a bulb and the current through that bulb.
Here are some sample measurements that you probably won't get, but if you look through here you should be able to understand the way that the voltage drops across the circuit and the current works its way through the circuit.
The brightness of a given bulb can essentially be measured in Watts (power usage), which you can find by multiplying the Voltage across a bulb and the current through that bulb.
Power and current and Voltage, oh my!
The block Wed/Thurs gives us some time to straighten out some of the different things we are learning about, as well as time to work on the labs.
Current activities:
* Labs up through #7,
* Energy Audit
* P=IV, V=IR homework
* Croc Physics Extra Credit
The quiz will be on Monday. The focus of the quiz will be the lab couple of electricity labs, and the Voltage homework (potential difference). For this quiz, you need to be able to reason through which light bulbs will be bright, and why. This involves understanding how resistance prevents the flow of electricity, how current can split to different pathways in a parallel branch, and how voltage "drops" across light bulbs as electricity goes around the circuit.
Voltage can be thought of as the "elevation" on Chutes and Ladders, batteries would be considered the ladders, and light bulbs would be the slides. Notice that some slides go from very high to very low, while others only make a small change. This would correspond to light bulbs that would be bright (large voltage change, thus a large current rushing through the bulb, providing tons of energy each second).
Tuesday, October 24, 2006
Energy and Power
Reminder that the Energy Audit, which I gave you two weeks ago, is due Friday 10/27.
This means that you need to keep track of all the things that you use in your house for a 24 hour period.
AND you need to examine an electrical bill, and your electric meter
Learn about reading the meter here:
http://www.dom.com/customer/vares_meter.jsp
(the image to the right has a reading of 01074 )
And here's a copy of my electric bill (an overestimation from a few months ago)
There are several factors to determining the total cost.
One is the actual cost divided by the total kWh used.
What dominion power prefers to do is take the "supply service" charge divided by the total kWh used. This way they can ignore the distribution service (which is also based on the amount used).
I used 2348 kWh of electricity in 32 days, and it costs me $174.96.
Thus, the cost was about 7.4 cents per kWh, and I used 73.4 kWh of electricity per day.
That is equivalent to having about 50 lightbulbs (60 Watts) turned on continuously.
OR, two space heaters running nonstop (1500 Watts)
There is also a homework assignment for resistance/power equation stuff coming up.
This means that you need to keep track of all the things that you use in your house for a 24 hour period.
AND you need to examine an electrical bill, and your electric meter
Learn about reading the meter here:
http://www.dom.com/customer/vares_meter.jsp
(the image to the right has a reading of 01074 )
And here's a copy of my electric bill (an overestimation from a few months ago)
There are several factors to determining the total cost.
One is the actual cost divided by the total kWh used.
What dominion power prefers to do is take the "supply service" charge divided by the total kWh used. This way they can ignore the distribution service (which is also based on the amount used).
I used 2348 kWh of electricity in 32 days, and it costs me $174.96.Thus, the cost was about 7.4 cents per kWh, and I used 73.4 kWh of electricity per day.
That is equivalent to having about 50 lightbulbs (60 Watts) turned on continuously.
OR, two space heaters running nonstop (1500 Watts)
There is also a homework assignment for resistance/power equation stuff coming up.
Static Electricity lab
Monday we did a short lab on static electricity.
We rubbed a plastic rod on a rabbit fur and examined the charge with an electroscope.
Here's a "virtual lab" demonstration of what we were seeing.
http://www.shep.net/resources/curricular/physics/P30/Unit2/electroscope.html
here's another, similar one, showing attraction via polarization:
http://physics.weber.edu/amiri/director/dcrfiles/electricity/pithBallS.dcr
We'll finish our discussion Tuesday about this phenomena:
1) polarization
2) charging by conduction
3) charging by induction
4) lightning rods
In short:
1) polarization -- the temporary rearrangement of charges in an object because of the influence of another charged object nearby.
2) charging by conduction -- direct transfer of charge by contact. (sparking, etc.) [A negatively charged rod, brought up and touching an electroscope will charge the scope negatively]
3) charging by induction -- indirect transfer of charge by first polarizing, and then grounding. (This results in the opposite charge).[a negatively charged rod brought near an electroscope will polarize it, meaning the negative charges already present in the electroscope will get pushed back. If we provide them a path out of the electroscope (a ground) they will leave. The net charge remaining on the electroscope will then be positive -- OPPOSITE the charge of the rod]
4) lightning rods - their primary job is to prevent lightning strikes, by helping to slowly trickle charges between sky/ground. A lightning cloud polarizes the ground, and buildings (etc.) thus appear to have the opposite charge of the cloud, thus making the building a very appealing target for a discharge of static charge. The lightning rod will slowly neutralize this imbalance, helping to prevent lightning strikes.
We rubbed a plastic rod on a rabbit fur and examined the charge with an electroscope.
Here's a "virtual lab" demonstration of what we were seeing.
http://www.shep.net/resources/curricular/physics/P30/Unit2/electroscope.html
here's another, similar one, showing attraction via polarization:
http://physics.weber.edu/amiri/director/dcrfiles/electricity/pithBallS.dcr
We'll finish our discussion Tuesday about this phenomena:
1) polarization
2) charging by conduction
3) charging by induction
4) lightning rods
In short:
1) polarization -- the temporary rearrangement of charges in an object because of the influence of another charged object nearby.
2) charging by conduction -- direct transfer of charge by contact. (sparking, etc.) [A negatively charged rod, brought up and touching an electroscope will charge the scope negatively]
3) charging by induction -- indirect transfer of charge by first polarizing, and then grounding. (This results in the opposite charge).[a negatively charged rod brought near an electroscope will polarize it, meaning the negative charges already present in the electroscope will get pushed back. If we provide them a path out of the electroscope (a ground) they will leave. The net charge remaining on the electroscope will then be positive -- OPPOSITE the charge of the rod]
4) lightning rods - their primary job is to prevent lightning strikes, by helping to slowly trickle charges between sky/ground. A lightning cloud polarizes the ground, and buildings (etc.) thus appear to have the opposite charge of the cloud, thus making the building a very appealing target for a discharge of static charge. The lightning rod will slowly neutralize this imbalance, helping to prevent lightning strikes.
Monday, October 23, 2006
VOLTAGE
The past week was a bit discombobulated with all the activities...
But here's the summary:
Voltage.
That was the main focus of discussion for the week.
Voltage, measured in Volts, is a measure of the
ELECTRIC POTENTIAL.
The units are Joules/Coulombs.
It is a measure of how much ooomph! each charge carries with it.
The analogies we have used are elevation, and pressure.
Imagine cliffs of various heights. A stream of water going over a small cliff will release a certain amount of energy as it crashes to the bottom.
The same stream of water going over a much higher cliff will release much more energy.
The stream of water is the current. The height of the cliff is the voltage.
If you don't have an elevation change, you won't get any stream of water at all.
And the bigger the cliff, the more "oomph" you get out of each gallon of water.
Voltage is like that.
Stack more batteries up, and you get a brighter lightbulb. This means greater oomph per charge, and it also means more charge will be flowing.
Of course it is a little different than that. But that gets us pretty far in understanding it. We also talk about "pressure", and can model a battery as a "pump" that pulls in water and pushes it out with energy.
Remember, the charges are already in the wire. The battery just pushes them around. Putting energy into the system by doing that.
The stronger the pump, the more charge you can move around, AND the more energy per charge.
We had two worksheets this past week on Voltage.
The first one is was examining the basic definitions of voltage, the other one was focusing on diagrams showing batteries and light bulbs where we consider the importance of "potential difference".
"Potential difference" is the term that we use for the difference in voltage between one side of the light bulb, and the other.
As we talked about in class, nobody is afraid of Kansas. Even though they are at 4000 ft above sea level. Since there is almost no variation in elevation, you don't have to worry about falling, or being caught in rapids. Same with electricity. No difference in voltage levels, means no current to flow.
This is why birds can perch on a high voltage power line without being electrocuted. But if they straddle two wires, at two different voltage levels, then they will provide a path for current to go from high to low, and they will fry. You can see this with squirrels trying to step from wire to pole, or kites connecting wire to ground with a piece of string. (Wet string, or metal string is best for conducting).
Ground is an important concept that we will keep developing. This is the "universal zero voltage level". The earth is a good "dumping ground" for charge.
But here's the summary:
Voltage.
That was the main focus of discussion for the week.
Voltage, measured in Volts, is a measure of the
ELECTRIC POTENTIAL.
The units are Joules/Coulombs.
It is a measure of how much ooomph! each charge carries with it.
The analogies we have used are elevation, and pressure.
Imagine cliffs of various heights. A stream of water going over a small cliff will release a certain amount of energy as it crashes to the bottom.
The same stream of water going over a much higher cliff will release much more energy.
The stream of water is the current. The height of the cliff is the voltage.
If you don't have an elevation change, you won't get any stream of water at all.
And the bigger the cliff, the more "oomph" you get out of each gallon of water.
Voltage is like that.
Stack more batteries up, and you get a brighter lightbulb. This means greater oomph per charge, and it also means more charge will be flowing.
Of course it is a little different than that. But that gets us pretty far in understanding it. We also talk about "pressure", and can model a battery as a "pump" that pulls in water and pushes it out with energy.
Remember, the charges are already in the wire. The battery just pushes them around. Putting energy into the system by doing that.
The stronger the pump, the more charge you can move around, AND the more energy per charge.
We had two worksheets this past week on Voltage.
The first one is was examining the basic definitions of voltage, the other one was focusing on diagrams showing batteries and light bulbs where we consider the importance of "potential difference".
"Potential difference" is the term that we use for the difference in voltage between one side of the light bulb, and the other.
As we talked about in class, nobody is afraid of Kansas. Even though they are at 4000 ft above sea level. Since there is almost no variation in elevation, you don't have to worry about falling, or being caught in rapids. Same with electricity. No difference in voltage levels, means no current to flow.
This is why birds can perch on a high voltage power line without being electrocuted. But if they straddle two wires, at two different voltage levels, then they will provide a path for current to go from high to low, and they will fry. You can see this with squirrels trying to step from wire to pole, or kites connecting wire to ground with a piece of string. (Wet string, or metal string is best for conducting).
Ground is an important concept that we will keep developing. This is the "universal zero voltage level". The earth is a good "dumping ground" for charge.
Monday, October 16, 2006
key terms
As we get deeper into electricity, we need to learn the important terminology to be able to discuss electrical stuff.
The BAD thing is that everyone has heard the terms, and almost NOBODY (including you, probably) knows what they mean.
Voltage, current, resistance, power.
All are technical terms that you must use correctly.
Current (I) we've talked about. Measured in Amps, it is the rate of flow of charge through a circuit.
Resistance (R) is the amount of resistance to flow. It can limit the amount of current, and also can cause the heating in things like filaments. Measured in ohms.
Voltage (V) is electric pressure. The greater the voltage, the greater the current.
The relationship between these variables is: I=V/R or V=IR
The key ingredient in voltage is the idea of DIFFERENCE. Nobody is afraid of Kansas. Even though it has an elevation (in the western side) as high as 4000 feet above sea level. The reason nobody is afraid, is that there isn't much elevation variation. Similarly with electricity. Only a DIFFERENCE in voltages really makes a difference. That's why we connect to the positive AND the negative. Just like (take a moment to let this sink in...) a waterfall needs to have a top AND a bottom. It won't work with just all the water at the top (hanging out in Kansas). It needs to have a bottom as well (a path to flow to).
Tomorrow, we'll start looking more into the concept of voltage, and learn some static electricity stuff.
The BAD thing is that everyone has heard the terms, and almost NOBODY (including you, probably) knows what they mean.
Voltage, current, resistance, power.
All are technical terms that you must use correctly.
Current (I) we've talked about. Measured in Amps, it is the rate of flow of charge through a circuit.
Resistance (R) is the amount of resistance to flow. It can limit the amount of current, and also can cause the heating in things like filaments. Measured in ohms.
Voltage (V) is electric pressure. The greater the voltage, the greater the current.
The relationship between these variables is: I=V/R or V=IR
The key ingredient in voltage is the idea of DIFFERENCE. Nobody is afraid of Kansas. Even though it has an elevation (in the western side) as high as 4000 feet above sea level. The reason nobody is afraid, is that there isn't much elevation variation. Similarly with electricity. Only a DIFFERENCE in voltages really makes a difference. That's why we connect to the positive AND the negative. Just like (take a moment to let this sink in...) a waterfall needs to have a top AND a bottom. It won't work with just all the water at the top (hanging out in Kansas). It needs to have a bottom as well (a path to flow to).
Tomorrow, we'll start looking more into the concept of voltage, and learn some static electricity stuff.
Thursday, October 12, 2006
Important info:
Quiz Friday. It will cover basic circuits, light bulbs, electric current, and circuit diagrams.
Current homework due Friday.
Energy Audit due Oct 27.
- You need to look at your household energy bill
- you need to look at your electric meter
- you need to record your energy usage for a 24 hour period.
- you may need to borrow one of the watt meters to measure your usage.
- I only have three of these, and there are 50 students. So start early, share nicely.
- No whining about the meter not being available on the last day!!!
Electric current:
So, wires are made of metal. Metal wire has bazillions of electrons in it already. If you try to put in just a few more on one end, then some pop out the other end. The voltage source (battery) is the pusher. Since the wires are already "full" of electrons, the "pulse", or "domino effect" is what is important. Almost at the speed of light, the signal travels across the wire, so the light turns on instantly. The electrons that are moving through the wire, actually travel slowly.
Since there are bazillions of electrons (like 10^18 or 1000000000000000000 electrons) moving through the wire each second in a standard lightbulb circuit. That's a lot.
So, Mr. Coulomb said: let's just take 10^18-ish electrons and call that "one Coulomb". Then we can talk about coulombs per second of electric current traveling through the wires.
Mr. Ampere said: "OK, we can call 1 Coulomb/sec an AMP". :-)
And thus, electric current is measured in Amps.
Circuit diagrams:
This is not a *Drawing* but rather a diagram. You've been looking at them for more than a week now in our lab write-ups. I have been going increasingly away from "pictoral" representations and towards schematic diagrams. The menu in croc physics that you used for your first Vlab is pictoral. Next to that menu is the schematic menu.
Here's a helpful link to become familiar with diagrams of electric circuits.
http://www.kpsec.freeuk.com/cdiags.htm
Tuesday, October 10, 2006
virtual physics lab
Today we were in the computer lab using "Crocodile Physics" simulation software.
We were working through a 4 page assignment that we will continue to work on in the Block period for a while Wed/Thurs.
The purpose of the simulations was to use some software to more quickly visualize the circuits that we have been building.
Most of the things that we do in the lab we can do in the simulation. Maybe not as fun... maybe more fun... than real life.
Certainly quicker to setup and measure with.
The focus of a lot of this is to gain a deeper understanding of electrical current (measured in Amps, or miliamps).
The other terms we are introducing are power (in Watts) and voltage (in Volts).
CAREFUL! People confuse these different terms a lot. Don't!
We will have a quiz on either Friday or Monday.
And we will continue to work on these labs for a while.
I will be putting a link to the croc physics software online so you can get a zip copy to try out at home. In the meantime, the software is available on the network at school, accesible from any computer in the school.
Here's a few places you can go for extra fun reading.
Besides your textbook...
try this: Physics Virtual Classroom
We were working through a 4 page assignment that we will continue to work on in the Block period for a while Wed/Thurs.
The purpose of the simulations was to use some software to more quickly visualize the circuits that we have been building.
Most of the things that we do in the lab we can do in the simulation. Maybe not as fun... maybe more fun... than real life.
Certainly quicker to setup and measure with.
The focus of a lot of this is to gain a deeper understanding of electrical current (measured in Amps, or miliamps).
The other terms we are introducing are power (in Watts) and voltage (in Volts).
CAREFUL! People confuse these different terms a lot. Don't!
We will have a quiz on either Friday or Monday.
And we will continue to work on these labs for a while.
I will be putting a link to the croc physics software online so you can get a zip copy to try out at home. In the meantime, the software is available on the network at school, accesible from any computer in the school.
Here's a few places you can go for extra fun reading.
Besides your textbook...
try this: Physics Virtual Classroom
Friday, October 06, 2006
electric circuits
The last part of the week we've been working on constructing basic electric circuits and trying to develop an understanding of what is going on inside the wire.
Lab #4 examined an electric switch in more detail, not as an "on/off" device, but rather as a way to complete a circuit or disconnect it. Then it continued by examining two light bulbs and a circuit that would test to see if electricity "got to one" faster than the other, and if "electricity was used up" or any silly notion like that. It turns out that energy is limited, so two bulbs glow dimmer than just one (when connected in series to a single battery) but the idea that a bulb "uses up a certain amount" and then there may/may not be any left for the other.... is wrong.
Lab #5 went even further to try to provide evidence for the idea that there is "something" moving through the wires, in a steady stream, throughout the entire circuit. The lab used a compass needle over top of the wire, and when electricity went through, the needle deflected a certain amount in a certain direction. The SAME exact thing happened in every part of the wire, which means that there isn't MORE of something at the beginning, and then it gets used up, like water flowing through a pipe, being let out in multiple places... Instead, whatever exits the battery, the same quantity of stuff goes back into the battery.
What we're learning is that electric current isn't "used up", but rather the charges moving around actually carry energy in the "wave" through the circuit.
But like a garden hose FULL of water, as soon as you turn on the tap, water flows out the far end. Wires are full of electrons already (they're metal!) so as soon as you put one in on one side, one pops out the other side.
Anyway, there's a homework assignment on basic circuit due on Friday also.
We'll be in the computer lab on Monday looking at "Crocodile Physics" circuit simulation software.
Lab #4 examined an electric switch in more detail, not as an "on/off" device, but rather as a way to complete a circuit or disconnect it. Then it continued by examining two light bulbs and a circuit that would test to see if electricity "got to one" faster than the other, and if "electricity was used up" or any silly notion like that. It turns out that energy is limited, so two bulbs glow dimmer than just one (when connected in series to a single battery) but the idea that a bulb "uses up a certain amount" and then there may/may not be any left for the other.... is wrong.
Lab #5 went even further to try to provide evidence for the idea that there is "something" moving through the wires, in a steady stream, throughout the entire circuit. The lab used a compass needle over top of the wire, and when electricity went through, the needle deflected a certain amount in a certain direction. The SAME exact thing happened in every part of the wire, which means that there isn't MORE of something at the beginning, and then it gets used up, like water flowing through a pipe, being let out in multiple places... Instead, whatever exits the battery, the same quantity of stuff goes back into the battery.
What we're learning is that electric current isn't "used up", but rather the charges moving around actually carry energy in the "wave" through the circuit.
But like a garden hose FULL of water, as soon as you turn on the tap, water flows out the far end. Wires are full of electrons already (they're metal!) so as soon as you put one in on one side, one pops out the other side.
Anyway, there's a homework assignment on basic circuit due on Friday also.
We'll be in the computer lab on Monday looking at "Crocodile Physics" circuit simulation software.
Tuesday, October 03, 2006
Electricity!!!
Welcome to our new topic!
Most of this week we are spending on introductory electricity labs.
These labs are meant to focus us on the basics and gain a thorough understanding of the basics of electricity.
lab #1: intro circuits
The core idea here is that you need a complete "circuit" or electrical loop in order for a bulb to light. The battery has two terminals, and so does the light bulb. The in-out path as shown in the diagram.
lab #2: conductors and insulators
Some materials (like wires) conduct electricity quite well. Other things, like plastic, don't.
This lab examines some materials to help you determine what conducts and what insulates, and what conducts sortof.
This will help us to understand how a light bulb is constructed in the next lab.
lab #3: how a lightbulb works.
In this lab we examine a few different light bulbs to try to gain an understanding of what is happening in them. The lab asks you to draw a cut-away view of a bulb so that you can see the various components and what is connected to what. 
Then test the pieces to see what are insulators and what are conductors.
Especially important is how the filament is connected to the base of the bulb.
You MUST show clearly how the TWO parts of the lightbulb base connect to the TWO ends of the filament.
The fourth lab will involve a more thorough understanding of what's going on in the wires.
Friday, September 29, 2006
end of waves.... here comes electricity
yeah Friday!
Well, the quiz didn't go so well for a few people.
But we had a healthy curve, so hopefully that helps dampen it a bit.
This first topic was sort of a "trial run" through a physics topic...
Things to learn for next time:
- when you hear a word repeated a few times, you'd better make sure you understand it.
(like frequency, etc.)
- Things that we talk about in class, things that are on the homework, and things that we do in lab all are important and will show up on the quizzes. While memorization is not a focus, understanding is. It is probably easier to memorize 100 words/definitions than to understand and calculate harmonics on a guitar string or in an organ pipe. Yet once you have learned how to do it, it really is pretty straightforward.
- Labs are part of the learning process. This is especially important in this next unit on electricity, where we have lots of labs that lead you through a process that is designed to help you learn on your own.
REPEAT: you are expected to learn by doing stuff in the lab. The lab is NOT just for writing stuff down and getting a grade. It is to increase your understanding of the material. So make sure your brain is ON.
The next unit, electricity, will start with some basic circuit stuff, and then continue to more complex things. We will use words that you have heard, but you probably don't really understand. So be careful. Voltage, current, resistance and power are some of the basics.
One activity that we will be doing is a "home energy audit" where you will need to track your energy usage over a 24 hour period. I have several meters to help you measure the electrical usage of different appliances, but we need to share them. So this assignment will be handed out early, so that we can line-up and check out the meters.
Have a nice weekend, we'll start fresh on Monday.
Well, the quiz didn't go so well for a few people.
But we had a healthy curve, so hopefully that helps dampen it a bit.
This first topic was sort of a "trial run" through a physics topic...
Things to learn for next time:
- when you hear a word repeated a few times, you'd better make sure you understand it.
(like frequency, etc.)
- Things that we talk about in class, things that are on the homework, and things that we do in lab all are important and will show up on the quizzes. While memorization is not a focus, understanding is. It is probably easier to memorize 100 words/definitions than to understand and calculate harmonics on a guitar string or in an organ pipe. Yet once you have learned how to do it, it really is pretty straightforward.
- Labs are part of the learning process. This is especially important in this next unit on electricity, where we have lots of labs that lead you through a process that is designed to help you learn on your own.
REPEAT: you are expected to learn by doing stuff in the lab. The lab is NOT just for writing stuff down and getting a grade. It is to increase your understanding of the material. So make sure your brain is ON.
The next unit, electricity, will start with some basic circuit stuff, and then continue to more complex things. We will use words that you have heard, but you probably don't really understand. So be careful. Voltage, current, resistance and power are some of the basics.
One activity that we will be doing is a "home energy audit" where you will need to track your energy usage over a 24 hour period. I have several meters to help you measure the electrical usage of different appliances, but we need to share them. So this assignment will be handed out early, so that we can line-up and check out the meters.
Have a nice weekend, we'll start fresh on Monday.
Tuesday, September 26, 2006
Review for the Wave quiz
Quiz is coming up on Wed/Thurs
You need to know lots of stuff.
This includes the homework and labs that we've done.
And class discussion stuff.
Scroll through the BLOG to see the topics and some tutorial stuff.
You may use a 3x5 notecard (both sides) with whatever you want on it. This includes equations, examples, diagrams, etc. As long as you write it out for yourself and turn it in with the quiz.
The packet that I gave you to study from has some great questions. Some things we didn't discuss, and sometimes we used different words. And sometimes we did stuff not covered in that text.
But it is a great place to go for lots of basic review problems.
Here are the answers (sorry the version is slightly different, so problems may be out of place a little).
http://www.yhspatriot.net/~aschuetz/subjects/waves/hewitt_answers/
good luck!!! I'll be in before school for any last minute questions you might have
You need to know lots of stuff.
This includes the homework and labs that we've done.
And class discussion stuff.
Scroll through the BLOG to see the topics and some tutorial stuff.
You may use a 3x5 notecard (both sides) with whatever you want on it. This includes equations, examples, diagrams, etc. As long as you write it out for yourself and turn it in with the quiz.
The packet that I gave you to study from has some great questions. Some things we didn't discuss, and sometimes we used different words. And sometimes we did stuff not covered in that text.
But it is a great place to go for lots of basic review problems.
Here are the answers (sorry the version is slightly different, so problems may be out of place a little).
http://www.yhspatriot.net/~aschuetz/subjects/waves/hewitt_answers/
good luck!!! I'll be in before school for any last minute questions you might have
Monday, September 25, 2006
Doppler and stuff
On Friday last week, we finished up (or got darn close to finishing up) the lab we were working on with sound waves.
We also discussed some other sound phenomena, specifically resonance.
We played with Chladni plates,
you can find a simulation here that is less "cool" but models the same behavior without the annoying sound. Some images are here
The homework handed out on Friday includes a question asking you to examine beat frequencies.
There are several good simulations out there to see/hear this.
Here's one to learn and hear the waves interacting: http://www.school-for-champions.com/science/soundbeat.htm though there is more math than you need.
Here's a good simulation to "see" the interference of the two waves:
http://www.mta.ca/faculty/science/physics/suren/Beats/Beats.html
Here's another great one, but you'll want to change the frequencies to lower values.
http://www.lon-capa.org/~mmp/applist/beats/b.htm
This one let's you type in "500 Hz" for the first, and then pick the difference (delta).
http://webphysics.davidson.edu/faculty/dmb/Beats/Beats.html?T1=500
But this one (finally!) is probably the most straight-forward for the assignment:
http://www.walter-fendt.de/ph11e/beats.htm
Monday, we discussed Doppler effect.
In water waves, in sound waves, specifically for high speed aircraft, and then also for doppler radar (weather stuff) and finally a concept called "galactic redshift" where we observe that light from distant galaxies are redder than we expect, indicating that they are all moving away from us (the doppler effect for light causes a shift in the spectrum (ROYGBIV) towards the red end when things are moving away from us).
Here's some good stuff for doppler effect:
great visuals: http://www.gmi.edu/~drussell/Demos/doppler/doppler.html
here's a make-your-own-doppler wave applet:
http://www.lon-capa.org/~mmp/applist/doppler/d.htm
and some more learnin' stuff:
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/waves/u10l3d.html
see video of mach1 flyby: http://www.kettering.edu/~drussell/Demos/doppler/mach1.mpg
read about it here: http://antwrp.gsfc.nasa.gov/apod/ap010221.html
We had a homework assignment that covered our discussion in class, and needs to be turned in before the quiz.
We also discussed some other sound phenomena, specifically resonance.
We played with Chladni plates,
you can find a simulation here that is less "cool" but models the same behavior without the annoying sound. Some images are here
The homework handed out on Friday includes a question asking you to examine beat frequencies.
There are several good simulations out there to see/hear this.
Here's one to learn and hear the waves interacting: http://www.school-for-champions.com/science/soundbeat.htm though there is more math than you need.
Here's a good simulation to "see" the interference of the two waves:
http://www.mta.ca/faculty/science/physics/suren/Beats/Beats.html
Here's another great one, but you'll want to change the frequencies to lower values.
http://www.lon-capa.org/~mmp/applist/beats/b.htm
This one let's you type in "500 Hz" for the first, and then pick the difference (delta).
http://webphysics.davidson.edu/faculty/dmb/Beats/Beats.html?T1=500
But this one (finally!) is probably the most straight-forward for the assignment:
http://www.walter-fendt.de/ph11e/beats.htm
Monday, we discussed Doppler effect.
In water waves, in sound waves, specifically for high speed aircraft, and then also for doppler radar (weather stuff) and finally a concept called "galactic redshift" where we observe that light from distant galaxies are redder than we expect, indicating that they are all moving away from us (the doppler effect for light causes a shift in the spectrum (ROYGBIV) towards the red end when things are moving away from us).
Here's some good stuff for doppler effect:
great visuals: http://www.gmi.edu/~drussell/Demos/doppler/doppler.html
here's a make-your-own-doppler wave applet:
http://www.lon-capa.org/~mmp/applist/doppler/d.htm
and some more learnin' stuff:
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/waves/u10l3d.html
see video of mach1 flyby: http://www.kettering.edu/~drussell/Demos/doppler/mach1.mpg
read about it here: http://antwrp.gsfc.nasa.gov/apod/ap010221.html
We had a homework assignment that covered our discussion in class, and needs to be turned in before the quiz.
Thursday, September 21, 2006
BLOCKS of Sound waves
during block day, Wed/Thurs we did 4 sound labs.
They used the computer interface (Lab Pro running Logger Pro).
We looked at:
1) the speed of sound using echoes in a long tube.
2) the wave patterns of tuning forks, captured with the microphone. We counted and measured the frequency, and compared it to the actual frequency of the tuning fork.
3) beat frequency, the pattern created by the interference of two tuning fork sound waves (see previous blog for more info).
4) the tones used by a touch-tone telephone to dial a phone number.
They used the computer interface (Lab Pro running Logger Pro).
We looked at:
1) the speed of sound using echoes in a long tube.
2) the wave patterns of tuning forks, captured with the microphone. We counted and measured the frequency, and compared it to the actual frequency of the tuning fork.
3) beat frequency, the pattern created by the interference of two tuning fork sound waves (see previous blog for more info).
4) the tones used by a touch-tone telephone to dial a phone number.
Beats and sound waves
On Tuesday we stoppped for a bit and reviewed any problems/issues/ equations/terms that people were willing to ask about.
Then we discussed "beats". We listened to two tuning forks that were slightly different in their frequencies. This caused the sound waves to reach our ears in such a way that occasionally they cancelled each other out, and other times they combined to a loud sound. The "wa-wa" sound of interference is known as the "beat" and the "beat frequency" is the number of "wa's" per second. This frequency ought to exactly match the frequency difference between the two forks.
If the image isn't moving, click here to see it animated.
Learn more about the "beat" phenomenon here
Then we looked at some more resonance stuff with the mechanical oscillator. We looked at metal sticks that would only resonate at specific frequencies. This is like a swing that will only swing back-and-forth at a certain rate. The shorter the rope, the more rapid will be the natural "resonance" frequency of its oscillation.
We also examined a metal hoop on the oscillator. When this hoop was vibrated from one end, the waves traveled both directions around the hoop. At just the right frequency, we got a standing wave pattern. This looked like the string resonator, but was wrapped around in a circle. The higher the frequency of oscillation, the more nodes/antinodes we would get on the hoop. This is actually a way of understanding the Bohr model of the atom that most of you learned about last year. Only certain conditions will allow for a stable resonance, and similarly in the Bohr atom, only certain orbits are stable, because electrons travel like waves around the nucleus. See photos here
Monday, September 18, 2006
Monday doesn't resonate with everyone
Well, today we had our first quiz.
Not only should it have not been a surprise for anybody who was there, but it should have been pretty easy considering it was based largely on the previous homework assignment, and almost identical to the review sheet I passed out on Friday.
Nonetheless, I know some students still haven't learned the basic terms/ideas that have been presented to them over the past few weeks.
So, now is a GREAT time to do something about it.
I am at school for generally 2 hours longer than you are. Before and after. And 5th period lunch is generally open for me (room 35 across the hall). So, please take some initiative if you are struggling. It is easier to get you back on track soon, than to wait and have a catastrophe on your hands later.
After the quiz we talked about two things.
1) refraction
2) resonance patterns (harmonics) on strings and in tubes.
First, refraction.
As waves change material, they change speed.
Since the frequency stays the same, the wavelength changes.
If this happens in water/air or with light at AN ANGLE, then the wave will enter the new material at a different angle. This process is called "refraction".
We looked at a simulation to help us visualize this.
Change the setup to Refraction (about halfway down the list).
You can also look at this explanation:
or check your textbook for more help.
We also examined standing wave patterns on strings. These different resonance patterns are called "harmonics" by music people.
The basic "types" of resonators we have are:
string - fixed at both ends
tube - open at one end
tube - open at both ends
the open ends would have anti-nodes, the fixed/closed ends would have nodes.
We looked at the basic progression of standing waves, such as you see in the picture here, which is from this site: http://www.phys.unsw.edu.au/~jw/flutes.v.clarinets.html and is discussing flutes (open-open) vs. clarinets (open - closed).
here's some technical junk on it: http://hyperphysics.phy-astr.gsu.edu/hbase/waves/string.html
but this might be easier to look at:
and
and again, your book is a good source for this stuff.
Friday, September 15, 2006
Resonance Friday
Today's class looked at a variety of resonance phenomenon.
Resonance is basically a continuous pattern of vibration in a material.
A swing is a basic example of this. It goes back and forth at a specific frequency, known as the resonance frequency.
Anything that vibrates does this.
A guitar string vibrating is another great example.
The basic mode of vibration is 1/2 of a wave fitting on the length of the string.
I can get a harmonic by encouraging it to vibrate with 11/2 the normal wavelength, so that an entire wave fits on the string.
Similar with instruments like bugels. By blowing harder, I can get more waves to fit inside the tube. A shorter wavelength means a higher frequency.
The answer to the practice quiz question #2 is f=0.2 Hz and T=5 sec
We also looked at a string being oscillated by a speaker/driver. If we reached resonance, we get a nice standing wave pattern. We can reach resonance at higher frequencies, too. The higher the frequency of resonance, the shorter the wavelength. So we have more nodes and antinodes.
Remember that each wavelength has two humps.
Numer three on the practice quiz is 1.5 m/s.
Go back a few days in the blog to see links for basic wave terminology and equations.
Number four, part c on the practice quiz has answers of f=6 Hz, v = 4 m/s, and lambda=0.38 m
See the solution from the previous homework for a radiowave problem solved like number five for the quiz.
In class we also examined several other resonances. Wine glasses, the plastic tube that you spin around to make sound, etc.
Be sure to be working through your book for various pictures, examples, and explanations.
Hope you have a nice weekend.
I'll be in Monday morning, probably half an hour before school starts if you have any last minute questions.
Resonance is basically a continuous pattern of vibration in a material.
A swing is a basic example of this. It goes back and forth at a specific frequency, known as the resonance frequency.
Anything that vibrates does this.
A guitar string vibrating is another great example.
The basic mode of vibration is 1/2 of a wave fitting on the length of the string.
I can get a harmonic by encouraging it to vibrate with 11/2 the normal wavelength, so that an entire wave fits on the string.
Similar with instruments like bugels. By blowing harder, I can get more waves to fit inside the tube. A shorter wavelength means a higher frequency.
The answer to the practice quiz question #2 is f=0.2 Hz and T=5 sec
We also looked at a string being oscillated by a speaker/driver. If we reached resonance, we get a nice standing wave pattern. We can reach resonance at higher frequencies, too. The higher the frequency of resonance, the shorter the wavelength. So we have more nodes and antinodes.
Remember that each wavelength has two humps.
Numer three on the practice quiz is 1.5 m/s.
Go back a few days in the blog to see links for basic wave terminology and equations.
Number four, part c on the practice quiz has answers of f=6 Hz, v = 4 m/s, and lambda=0.38 m
See the solution from the previous homework for a radiowave problem solved like number five for the quiz.
In class we also examined several other resonances. Wine glasses, the plastic tube that you spin around to make sound, etc.
Be sure to be working through your book for various pictures, examples, and explanations.
Hope you have a nice weekend.
I'll be in Monday morning, probably half an hour before school starts if you have any last minute questions.
Thursday, September 14, 2006
Block waves
Wed/Thurs physics block.
Yeah double physics!!!
We did lots of things in this class.
First, we finished the second slinky lab.
Then we talked about the lab: standing waves, medium determines the speed, etc.
We discussed the terms "node" and "anti-node" and saw the visual of the bugel playing, with a representation of the nodes/anti-nodes (click the "physics" button on the bottom to display)
We saw the video clip of "slinky football", showing different slinky/spring waves traveling across a surface. The interesting part was when one slinky was stretched out, and one was looser, the wave traveled faster in the tight one. Then we looked at three different materials (garden hose, slinky, and brass spring). We saw that each material, stretched that distance, had a different speed.
Next, we looked at water waves in the ripple tank, and examined a "moire" pattern on a small handout (circles on paper and transparency sheet, overlapping).
A few simulations showing this:
http://www.walter-fendt.de/ph11e/interference.htm
http://www.falstad.com/ripple/ (adjust the simulation to "2 sources, 1 frequency")
We listened to this same phenomenon happening with sound waves, pumping an annoying tone through the classroom, out of two speakers. The waves interfered with each other, sometimes making a loud sound, sometimes cancelling out.
We then worked on a homework assignment, drawing wave superposition witih triangle and square waves.
See more wave superposition: http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=35
and even more: http://www.kettering.edu/~drussell/Demos/superposition/superposition.html
Last, I handed out a homework assignment and talked about the first few problems (car suspension and blinker synchronization). This homework will probably be taken up on Monday.
wave superposition homework should be done-ish by Friday. If you have questions, we can address those and I'll take the work on Monday.
Friday we'll look at standing waves on a string, and more sound/instrument related phenomena.
Yeah double physics!!!
We did lots of things in this class.
First, we finished the second slinky lab.
Then we talked about the lab: standing waves, medium determines the speed, etc.
We discussed the terms "node" and "anti-node" and saw the visual of the bugel playing, with a representation of the nodes/anti-nodes (click the "physics" button on the bottom to display)
We saw the video clip of "slinky football", showing different slinky/spring waves traveling across a surface. The interesting part was when one slinky was stretched out, and one was looser, the wave traveled faster in the tight one. Then we looked at three different materials (garden hose, slinky, and brass spring). We saw that each material, stretched that distance, had a different speed.
Next, we looked at water waves in the ripple tank, and examined a "moire" pattern on a small handout (circles on paper and transparency sheet, overlapping).
A few simulations showing this:
http://www.walter-fendt.de/ph11e/interference.htm
http://www.falstad.com/ripple/ (adjust the simulation to "2 sources, 1 frequency")
We listened to this same phenomenon happening with sound waves, pumping an annoying tone through the classroom, out of two speakers. The waves interfered with each other, sometimes making a loud sound, sometimes cancelling out.
We then worked on a homework assignment, drawing wave superposition witih triangle and square waves.
See more wave superposition: http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=35
and even more: http://www.kettering.edu/~drussell/Demos/superposition/superposition.html
Last, I handed out a homework assignment and talked about the first few problems (car suspension and blinker synchronization). This homework will probably be taken up on Monday.
wave superposition homework should be done-ish by Friday. If you have questions, we can address those and I'll take the work on Monday.
Friday we'll look at standing waves on a string, and more sound/instrument related phenomena.
Tuesday, September 12, 2006
the medium determines the speed
This is the "moral" of the activities that we are doing.
We are examining the relationship between velocity, frequency, and wavlength.
The speed does not depend on the frequency.
The speed does not depend on the wavelength.
The speed only depends on the material.
So if you change the material (different spring, different tension) the speed will change.
If you increase the frequency (shake your hand faster) it does NOT change the speed.
What it DOES do, is decrease the wavelength.
Class today was a little disombobulated because of the modified schedule for class meetings.
Hope you enjoyed them. During class we worked on finishing up the lab, and talked a little about "nodes" and "anti-nodes".
Wed/Thurs during block we'll work more on wave interactions. Interference and standing waves. We'll look at water waves, listen to sound waves, and see some computer generated waves.
Here's another great website that shows lots of the stuff we've been working on:
http://id.mind.net/~zona/mstm/physics/waves/waves.html
We are examining the relationship between velocity, frequency, and wavlength.
The speed does not depend on the frequency.
The speed does not depend on the wavelength.
The speed only depends on the material.
So if you change the material (different spring, different tension) the speed will change.
If you increase the frequency (shake your hand faster) it does NOT change the speed.
What it DOES do, is decrease the wavelength.
Class today was a little disombobulated because of the modified schedule for class meetings.
Hope you enjoyed them. During class we worked on finishing up the lab, and talked a little about "nodes" and "anti-nodes".
Wed/Thurs during block we'll work more on wave interactions. Interference and standing waves. We'll look at water waves, listen to sound waves, and see some computer generated waves.
Here's another great website that shows lots of the stuff we've been working on:
http://id.mind.net/~zona/mstm/physics/waves/waves.html
Monday, September 11, 2006
slinky - part two
Today we worked through some of the math problems and talked about the homework.
Some students had me examine their paper, then they'll finish it at home and turn it in tomorrow.
We started another slinky lab today. We'll finish it on Tuesday.
The purpose of the lab is to examine more of the relationships and behavior of waves.
First, vel = freq x wavelength
Second, the effect of the material on the wave speed, freq, wavelength
Third, the pattern of a "standing wave", when a wave travels down the spring, bounces off the end, comes back, and collides with the waves that are traveling down the spring. The standing wave pattern has "nodes" and "anti-nodes" . A full wavelength, includes two "humps".
Take a look at this tutorial stuff, if you would like more words, etc.
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/waves/u10l4c.html
here's another site with good graphics, but it gets a little more complicated than what we're doing: http://hyperphysics.phy-astr.gsu.edu/hbase/waves/standw.html
no new homework today, but some people are finishing their previous one. We'll finish the lab tomorrow, and maybe get one more assignment (with time in class to work).
Some students had me examine their paper, then they'll finish it at home and turn it in tomorrow.
We started another slinky lab today. We'll finish it on Tuesday.
The purpose of the lab is to examine more of the relationships and behavior of waves.
First, vel = freq x wavelength
Second, the effect of the material on the wave speed, freq, wavelength
Third, the pattern of a "standing wave", when a wave travels down the spring, bounces off the end, comes back, and collides with the waves that are traveling down the spring. The standing wave pattern has "nodes" and "anti-nodes" . A full wavelength, includes two "humps".
Take a look at this tutorial stuff, if you would like more words, etc.
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/waves/u10l4c.html
here's another site with good graphics, but it gets a little more complicated than what we're doing: http://hyperphysics.phy-astr.gsu.edu/hbase/waves/standw.html
no new homework today, but some people are finishing their previous one. We'll finish the lab tomorrow, and maybe get one more assignment (with time in class to work).
Friday, September 08, 2006
more waves AND homework help
Friday... We plowed through the key definitions, looked at some video clips (I'm putting them onto the website soon, so look online if you are interested in seeing them again).
The homework is due Monday. We didn't have time to work through numerical examples, but do your best.
Here's a few answers that might help:
2d) one wave every two seconds, means 1 wave/2 sec = 0.5 waves/sec
2e) use the frequency of the above problem (f=0.5 Hz), use the given speed v= 3 m/s. Use the equation velocity= frequency x wavelength --> so wavelength = velocity/frequency = 3 m/s / 0.5 waves/sec = 6 meters/wave.
Notice that the UNITS are all in there.
4d) Radio waves travel at the speed of light. v=3 x 10^8 m/s. The frequency is 85.5 MHz, which is 8.55 x 10^7 Hz (85.5 x 10^6 Hz). So, velocity= frequency x wavelength --> so wavelength = velocity/frequency = (3 x 10^8 m/s )/ (8.55 x 10^7 cycles/sec) = 3.5 m/cycle
So the wavelength is 3.5 meters long.
5c) this is kinda a trick question. the velocity is determined by the medium, not the frequency.
The homework is due Monday. We didn't have time to work through numerical examples, but do your best.
Here's a few answers that might help:
2d) one wave every two seconds, means 1 wave/2 sec = 0.5 waves/sec
2e) use the frequency of the above problem (f=0.5 Hz), use the given speed v= 3 m/s. Use the equation velocity= frequency x wavelength --> so wavelength = velocity/frequency = 3 m/s / 0.5 waves/sec = 6 meters/wave.
Notice that the UNITS are all in there.
4d) Radio waves travel at the speed of light. v=3 x 10^8 m/s. The frequency is 85.5 MHz, which is 8.55 x 10^7 Hz (85.5 x 10^6 Hz). So, velocity= frequency x wavelength --> so wavelength = velocity/frequency = (3 x 10^8 m/s )/ (8.55 x 10^7 cycles/sec) = 3.5 m/cycle
So the wavelength is 3.5 meters long.
5c) this is kinda a trick question. the velocity is determined by the medium, not the frequency.
Thursday, September 07, 2006
waves stuff
Today we tested our theories on the speed of a slinky wave.
We had lots of good experiments, some of them found no appreciable difference between their variable and the wave speed. For example, the size of the wave pulse, or the frequency of the pulse did not affect the speed.
But the one factor that did, was to change the medium. In other words, the material.
In this case, we are talking about the slinky. Stretching the slinky more/less caused the wave speed to change. This is a general property of waves.
We discussed the example of sound waves traveling through different air (hot/cold or nitrogen vs. helium). We also talked about water waves, and how the speed slowed as the water got shallower and they "crashed" on the shore.
We discussed some of the major wave terminology: Amplitude, wavelength, frequency, period, and of course wave speed (or velocity).
You can find some nice tutorial stuff here:
http://www.physicsclassroom.com/Class/waves/wavestoc.html
There was homework handed out today.
It is due on Monday.
Come with questions on Friday, where we'll talk more about wave terminology and a few equations, and see a few other slinky things.
We had lots of good experiments, some of them found no appreciable difference between their variable and the wave speed. For example, the size of the wave pulse, or the frequency of the pulse did not affect the speed.
But the one factor that did, was to change the medium. In other words, the material.
In this case, we are talking about the slinky. Stretching the slinky more/less caused the wave speed to change. This is a general property of waves.
We discussed the example of sound waves traveling through different air (hot/cold or nitrogen vs. helium). We also talked about water waves, and how the speed slowed as the water got shallower and they "crashed" on the shore.
We discussed some of the major wave terminology: Amplitude, wavelength, frequency, period, and of course wave speed (or velocity).
You can find some nice tutorial stuff here:
http://www.physicsclassroom.com/Class/waves/wavestoc.html
There was homework handed out today.
It is due on Monday.
Come with questions on Friday, where we'll talk more about wave terminology and a few equations, and see a few other slinky things.
Wednesday, September 06, 2006
Intro to waves
Today we talked briefly about data collection (stopwatch activity)
Then worked on the first few parts of the slinky lab.
Everybody did a great job NOT screwing up the slinkies. Let's hope that the other 6 classes do as well as you did! (We'll find out tomorrow when we pull the slinkies out again!)
Homework for tonight is to prepare your experiment for tomorrow. Devise a method to test the effects of
Tuesday, September 05, 2006
First day of class
Well, first day has come and gone.
Looks like it will be a fun year!
Here's what we did:
1) syllabus and discussion about course policies and guidelines.
2) short survey (hand in)
3) name physics-stuff, and get-to-know you activity.
4) a few demos
Come back for more!
Remember, if you have any questions/concerns/ please let me know.
you can stop by class, or send me an e-mail. schuetz.physics@gmail.com
Welcome to class!!!
Looks like it will be a fun year!
Here's what we did:
1) syllabus and discussion about course policies and guidelines.
2) short survey (hand in)
3) name physics-stuff, and get-to-know you activity.
4) a few demos
Come back for more!
Remember, if you have any questions/concerns/ please let me know.
you can stop by class, or send me an e-mail. schuetz.physics@gmail.com
Welcome to class!!!
Wednesday, August 30, 2006
Classes breakdown
I just received my class lists.
24 students in first period
24 students in second period.
Looks like a good sized group!
Along with more than 75 students in my three intensified physics classes, I've got a few names to learn.
So bear with me as I get to know each of you.
Please feel free to drop me an e-mail at schuetz.physics@gmail.com if you have any comments or concerns, or want me to be aware of anything "interesting" about you early on.
(Like that you have 6 fingers on your right hand, or that your mother only allows you to wear outfits with pictures of teddy bears on them, or that there is a certain student who you really shouldn't sit next to, because you have a hard time making good decisions around them, and you don't want to get in trouble in class).
24 students in first period
24 students in second period.
Looks like a good sized group!
Along with more than 75 students in my three intensified physics classes, I've got a few names to learn.
So bear with me as I get to know each of you.
Please feel free to drop me an e-mail at schuetz.physics@gmail.com if you have any comments or concerns, or want me to be aware of anything "interesting" about you early on.
(Like that you have 6 fingers on your right hand, or that your mother only allows you to wear outfits with pictures of teddy bears on them, or that there is a certain student who you really shouldn't sit next to, because you have a hard time making good decisions around them, and you don't want to get in trouble in class).
Thursday, August 24, 2006
Welcome to Physics!
Hello students!
I decided to try running a "Blog" for my regular physics classes this year.
The idea is that this blog will be an easy place for me to list activities, post information, answers, pictures, and other material. It is easier/quicker than building pages for the school's website, and it also allows you to make comments on the entries.
Please give me feedback on this effort and let me know what you think would make this a useful tool to help you enjoy physics and succeed in the course!
thanks, and I'm looking forward to an exciting year!
Mr. Schuetz
I decided to try running a "Blog" for my regular physics classes this year.
The idea is that this blog will be an easy place for me to list activities, post information, answers, pictures, and other material. It is easier/quicker than building pages for the school's website, and it also allows you to make comments on the entries.
Please give me feedback on this effort and let me know what you think would make this a useful tool to help you enjoy physics and succeed in the course!
thanks, and I'm looking forward to an exciting year!
Mr. Schuetz
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