Test Prep for AP® Courses

7.2 Production of Electromagnetic Waves


If an electromagnetic wave is described as having a frequency of 3 GHz, what are its period and wavelength (in a vacuum)?

  1. 3.0 × 109s, 10 cm
  2. 3.3 × 10−10s, 10 cm
  3. 3.3 × 10−10s, 10 m
  4. 3.0 × 109s, 10 m

Describe the outcome if you attempt to produce a longitudinal electromagnetic wave.


A wave is travelling through a medium until it hits the end of the medium and there is nothing but vacuum beyond. What happens to a mechanical wave? Electromagnetic wave?

  1. Reflects backward, continues on
  2. Reflects backward, reflects backward
  3. Continues on, continues on
  4. Stops, continues on

You’re on the moon, skipping around, and your radio breaks. What would be the best way to communicate this problem to your friend, who is also skipping around on the moon: Yelling or flashing a light? Why?


Given the waveform in Figure 7.5(d), if T=3.0×109sT=3.0×109s and E=5.0×105N / CE=5.0×105N / C, which of the following is the correct equation for the wave at the antenna?

  1. (5.0×105N / C)sin(2π(3.0×109s)t)(5.0×105N / C)sin(2π(3.0×109s)t)
  2. (5.0×105N / C)sin(2πt(3.0×109s))(5.0×105N / C)sin(2πt(3.0×109s))
  3. (5.0×105N / C)cos(2π(3.0×109s)t)(5.0×105N / C)cos(2π(3.0×109s)t)
  4. (5.0×105N / C)cos(2πt(3.0×109s))(5.0×105N / C)cos(2πt(3.0×109s))

Given the waveform in Figure 7.5(d), if f=2.0f=2.0 GHz and E=6.0×105N/CE=6.0×105N/C, what is the correct equation for the magnetic field wave at the antenna?


In Heinrich Hertz’s spark gap experiment (Figure 7.4), how will the induced sparks in Loop 2 compare to those created in Loop 1?

  1. Stronger
  2. Weaker
  3. Need to know the tuner settings to tell
  4. Weaker, but how much depends on the tuner settings

The sun is far away from Earth, and the intervening space is very close to empty. Yet the tilt of Earth’s axis of rotation relative to the sun results in seasons. Explain why, given what you have learned in this section.

7.3 The Electromagnetic Spectrum


The correct ordering from least to greatest wavelength is

  1. ELF, FM radio, microwaves, infrared, red, green, ultraviolet, X-ray, gamma ray
  2. ELF, FM radio, microwaves, infrared, green, red, ultraviolet, X-ray, gamma ray
  3. gamma ray, X-ray, ultraviolet, red, green, infrared, microwaves, FM radio, ELF
  4. gamma ray, X-ray, ultraviolet, green, red, infrared, microwaves, FM radio, ELF

Describe how our vision would be different if we could see energy in what we define as the radio spectrum.

7.4 Energy in Electromagnetic Waves


An old microwave oven outputs only half the electric field it used to. How much longer does it take to cook things in this microwave oven?

  1. Four times as long
  2. Twice as long
  3. Half the time
  4. One fourth the time

Describe at least two improvements you could make to a radar set to make it more sensitive (able to detect things at longer ranges). Explain why these would work.