## Due 3:30 pm, Thursday, December 3rd

Physics 105, Fall Term, 2009

Did you complete the reading assignment?

Yes
No

## KEY CONCEPTS:

1) The speed of a wave is the product of its wavelength and frequency.

2) Waves reflect and refract at boundaries between media.

3) When two or more waves occupy the same spot in a medium they interfere with each other.

A wave is the transfer of energy through a medium created by a disturbance in that medium. To learn about some of the properties and behaviors of waves, go to: http://phet.colorado.edu/sims/wave-on-a-string/wave-on-a-string_en.html.

Click on the wrench and quickly drag it up and then back in place. What is the medium of the wave?

The wrench
The string
The clamp

Change the 'Damping' to zero near the top of the screen. Also change the 'Tension' to its medium setting and select 'No End' near the bottom right of the applet. Change the drive setting to 'Oscillate' near the lower left of the applet and then change the 'Frequency' option that appears at the top of the applet to 20 Hz. Press the 'Reset' button at the bottom left to make things easier to see.

Now decrease the frequency to 10 Hz. What happens to the wavelength when the frequency is decreased?

Wavelength gets longer
Wavelength gets shorter
Wavelength stays the same

What happens to the speed of the wave when the frequency is decreased?

Speed increases
Speed decreases
Speed stays the same

Now increase the tension to its maximum amount. What happens to the wavelength when the tension is increased?

Wavelength gets longer
Wavelength gets shorter
Wavelength stays the same

What happens to the speed of the wave when the the tension is increased?

Speed increases
Speed decreases
Speed stays the same

What determines the speed of a wave?

The frequency
The wavelength
Properties of the medium

Now change to the 'Pulse' option near the lower left of the applet. Change to a 'Fixed End' at the lower right side of the applet, then press the green 'Pulse' button under the reset button. The clamp acts as a rigid, more dense medium in this situation. What happens when a wave comes to the barrier between mediums?

Now change to a 'Loose End' and click the 'Reset' and then 'Pulse' buttons. The ring around the pole acts as a non-rigid, less dense medium in this situation. How is a wave's behavior when it reaches the barrier to a less dense medium different from when it reaches the barrier to a more dense medium?

Now add another pulse to the string when the first pulse is at the end with the ring and pole. Then turn the tension in the rope down enough so that you can clearly see what is happening when the pulses get to the same point on the string. When the pulses get to the same point on the string, it is called interference.

What happens when the pulses get to the same point on the string when they are on the same side of the string?

The pulses form 1 big wave and travel together as 1 big wave afterwards.
The pulses disappear because they cancel each other out.
The pulses form 1 big wave for a short while and then continue on their separate motion as though they never interacted with the other pulse.
The pulses disappear for a short while and then continue on their separate motion as though they never interacted with the other pulse.

What happens when the pulses get to the same point on the string when they are on opposite sides of the string?

The pulses form 1 big wave and travel together as 1 big wave afterwards.
The pulses disappear because they cancel each other out.
The pulses form 1 big wave for a short while and then continue on their separate motion as though they never interacted with the other pulse.
The pulses disappear for a short while and then continue on their separate motion as though they never interacted with the other pulse.

FEEDBACK

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Was there anything that you didn't understand in the reading assignment?  What was confusing to you?