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.

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

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.

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.

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 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:

http://www.physicsclassroom.com/Class/refrn/U14L1a.html

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:

http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/sound/u11l4c.html

and

http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/sound/u11l4d.html

and again, your book is a good source for this stuff.

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.