Assessment
https://cms.psu.edu/Section/Assessment/Delivery/AssessmentAl...
1.
2.
Waves tend to bend to the side
A) With slower wave velocity
B) with higher wave velocity
C) that is upward
D) that is downward
Lets first start with two quick questions about waves.
The fastest sound wave is:
A) Low Frequency
B) middle frequency (voice)
C) High frequency
D) they all travel at the same speed.
3.
Start the simulation
PROCEDURE:
1. Download and open the simulation http://phet.colorado.edu/en/simulation/wave-interference
2. Keeping the water tab. Move the frequency marker and amplitude marker to the center of their scales.
3. Click on “Show Graph”. This shows a side view of the ripples leaving the disturbance caused by the drop of water.
4. Click on the measuring tape box. The placement of the two red x’s are used to measure the wavelength (λ).
5. Click on “Add Detector”. This gives you the ability to determine the number of waves passing in a second (f).
6. Drag the “Measuring Tape”, and the “Detector” to the white area out of the water.
BEFORE YOU CHANGE ANYTHING ELSE!
7. Click Pause, move the marker on “ROTATE VIEW to SIDE”. Using the measuring tape, Place the red
cross under Phet on top of a crest first, then move the other red cross to the top of the next
crest. The centimeters in the green box is the wavelength. Record the distance in centimeters (λ (write the
units).
1.75 cm
4.
Move the marker on “ROTATE VIEW back to TOP”.
Click Play. Use the Detector to determine the number of complete waves that occur each second. (HINT: Each block
in the Detector is one second.) Record the number of waves per second (cycles per second) or Hertz (Hz) (f)
1.5 Hz
5.
Using the frequency and wavelength data that you collected, calculate the velocity. SHOW AND EXPLAIN YOUR
WORK below. Use UNITS ON ALL NUMBERS!
v = wavelength times frequency. so the speed of the wave v = (1.75 cm) * 1.5 Hz = 2.625 cm/s
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6.
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9/16/13 12:04 PM
Assessment
https://cms.psu.edu/Section/Assessment/Delivery/AssessmentAl...
REFLECTION
1. Click the off button on the faucet.
2. Add a vertical wall (bottom right corner) across the entire width of the tank by clicking on “One Slit” then adjusting
the “Slit Width” to zero.
3. Move the ‘Barrier Location” marker to 6.2 cm.
4. Click the ON button on the faucet. Click PAUSE after the wave returns back to the faucet. Describe the wave
pattern in complete sentences below. Compare between the no wall and wall pattern.
--No wall: nice circular ring moving clearly to the right.
-- with wall the rings are broken with black and blue patches. It looks like a square pattern shirt
but the squares always move.
--when you just set up the wall, you can tell that the wave moves right, bounces back to the left
and "add" to the incoming waves
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7.
Light
Consider the four pictures shown below, showing pure yellow lights shining toward a screen. In 3 and 4, there is a solid
wall between the light and screen, with one or two slits cut in to let the light through.
Compare the four scenarios. We are interested in your ideas about what is going on – you will only be graded for effort
here. What do you think might be happening to the light to create these different patterns?
1. just one normal light that spreads out.
2. With two light, the two sources interact and you get 2 places where no light go
3. with a small slit, the light spread out but it more concentrated than with no slits (Q1)
4. With two slits. Its like #2. Each slit acts like a light and so again I see places where the
wave interacted and we have a zero.
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8.
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Color
9/16/13 12:04 PM
Assessment
https://cms.psu.edu/Section/Assessment/Delivery/AssessmentAl...
Go the light tab in the simulation abd get a feel for the controls.
1. Move the wavelength marker to purple and click “Play”.
the measuring tape.
Measure the wavelength between two crests with
2. Move the wavelength marker to bright red and make the wavelength measurement again.
3. Write the two values for the wavelenght below. What conclusion/inference can you make about the wavelengths of
color? Compare to the size of an atom, how small or big is the wavelength of light?
purple, wavelength is 446.69 nm
red, wavelength is 678.73 nm
Different wavelength of light means different colors. Red is the biggest wavelength and it becomes
smaller for all the other colors in the order of the rainbow.
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9.
Try to recreate the pictures shown in Question 7 above with the simulation. Describe what you had to do with the
simulation to reproduce each of the pictures. Hint: use Bright red for color and push the amplitude to maximum
1.
2.
3.
4.
to
need to push show screen and wait.
push two light buttons
back to one light, push on one slit.
push on two slits. That one was harder, I had to adjust the slit width and the slit separation
get the pattern to match.
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10. Compare what you learned from the simulation to your ideas from question 7. What ideas would you keep? What ideas
would you change? (Did you notice the third bright spot right behind the wall in case 4?)
Looks like I was pretty good. The bright spot behind the wall in case 4 is weird though.
I guess that if I think of of each slit as a source of light then they should emit light behind the
wall.
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11.
In case 2, what happens to the pattern on the screen when the lights are brought closer to each other or farther apart?
Make sure to wait long enough for the pattern to change on the screen.
When the lights are further apart, the black lines on the screen get closer to each other. More
lines appears as well. I got 4 lines to appear.
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12. In case 4, what happens to the pattern when the slits are brought closer and farther apart?
Its more faint but same thing as before. With the two slits farther away, the black lines are
closer to each other and there is more of them.
Essentially, 2 slits is just like two light sources.
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Done
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