Physics 221
Lab 5
Electromagnetic Waves – An exploration
Prediction
1. Please explain what an electromagnetic wave is. Give as many examples as you know. Please
place the different types in some sort of order that you define.
Visible Light
You will use the PhET simulation Wave Interference for the following three questions.
1. Play with the first tab, “Water.”
a. Try adding a detector. Explain what this is showing.
b. Why does the amplitude of the waves drop off the further you are from the faucet?
What is this called?
c. What do you see when you rotate the view?
2. Play with the second tab, “Sound.”
a. Try adding a detector. Explain what this is showing.
b. Are the sound waves attenuating? Why is this?
c. Could the graph on the detector have a different label on the y axis and still have the
same shape? What other graph could be shown that would still look like a sine wave?
d. What do you see when you rotate the view? Why doesn’t it look different from the top
versus from the side?
e. What are the particles representing in the “Particle view”?
f. Do the particles move across the screen from the speaker all the way to the right side?
Explain why.
g. Set the frequency slider at a moderately low frequency so that you can easily take
measurements with this graph. Determine the wavelength, wave speed and frequency
of the sound wave.
h. Are your results reasonable? Would this be a low sound or a high sound?
3. Play with the 3rd tab, “light.”
a. Try adding a detector. Explain what you think this graph might be showing.
b. What do you see when you rotate the view? Why doesn’t it look different from the top
versus from the side?
c. What does changing the amplitude slider do to the light?
d. What does the screen show?
e. Add a mirror – what does this do to the light? What is analogous to adding a mirror on
the sound tab? Explain why.
f. Calculate the wavelength, wave speed and frequency of the light. Determine the
frequency range of the light shown (show your calculations).
Radio Waves
Use the PhET simulation Radio Waves for the following questions.
4. Play with everything in this simulation.
a. Now that you’ve investigated the entire simulation consider the “radiated field”.
Describe what the “curve with vectors” is representing. What is the curve and what are
the vectors?
b. Now describe what the full field view is representing.
c. What is creating the electric field?
d. Roughly how long is a mid-frequency wavelength in this sim based on the background
graphics? Using your estimate and the speed of radio waves to be 3 x 108 m/s, calculate
the frequency of a mid-frequency radio wave.
Microwaves
Use the PhET simulation Microwaves for the following questions.
5. Play with all four tabs
a. What is the difference between the “Field Views”. Describe what each is showing.
b. What type of molecules do you think are being shown?
c. How do they react as they heat up?
d. How does the microwave behave differently on 50% power or 25% power?
e. Google the frequency range of microwaves. What do you suppose the unit on the
frequency slider in this sim must be? Why?
X-rays
6. X-rays have wavelengths ranging from 0.01 to 10 nanometers. If the speed of an x-ray is 3 x 108
m/s, calculate the frequency range for x-rays.
Electromagnetic Waves
7. Make a 1-D graph of frequencies. The axis will be frequencies in terms of powers of 10. 104 Hz,
105 Hz , 106 Hz etc… Mark your frequency range for radio waves, microwaves, visible light and xrays on your graph.
8. Visit the Electromagnetic Spectrum page and Wikipedia. Enlarge the diagram on the top right
and check to see if your 1-D graph matches up with their graph of frequency.
9. What types of electromagnetic radiation are on their graph but not on yours?