Practice Electromagnetic Waves in Physics

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

Transverse waves consisting of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of propagation.

Light, radio, X-rays—all are EM waves, just different frequencies.

Showing a random 20 of 50 problems.

Example 1

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How long does light take to travel 1 km1\,\text{km} in vacuum?

Example 2

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Why can sound waves NOT travel through vacuum, but light can?

Example 3

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In what medium can electromagnetic waves travel that sound waves cannot?

Example 4

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An EM wave travels through a material at v=1.5×108 m/sv = 1.5\times10^8\,\text{m/s}. Find the refractive index nn.

Example 5

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A laser pulse travels 9×108 m9 \times 10^8 \text{ m} through vacuum. How long does it take?

Example 6

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A microwave oven operates at a frequency of 2.45×109 Hz2.45 \times 10^9 \text{ Hz}. What is the wavelength of the microwaves? Use c=3×108 m/sc = 3 \times 10^8 \text{ m/s}.

Example 7

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An EM wave has frequency 5×109 Hz5\times10^9\,\text{Hz}. Find its wavelength in vacuum.

Example 8

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A microwave has frequency f=3×109 Hzf = 3 \times 10^9 \text{ Hz}. Find its wavelength in vacuum (in cm).

Example 9

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An EM wave has frequency f=2×1014f = 2 \times 10^{14} Hz. What is its period?

Example 10

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A pulsed EM source emits at f=1×109f = 1\times10^9 Hz. In one period, how far does the wave front advance in vacuum?

Example 11

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In a glass of refractive index n=1.5n = 1.5, an EM wave originally at λ=600 nm\lambda = 600\,\text{nm} enters. Find the wavelength in glass (frequency stays the same).

Example 12

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A radar beam travels to a plane 30 km30\,\text{km} away and reflects back. Find the round-trip time.

Example 13

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A blue light enters glass. What happens to its frequency?

Example 14

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An EM wave's electric field amplitude is E0=600 V/mE_0 = 600\,\text{V/m}. Find the magnetic field amplitude B0B_0.

Example 15

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Do all electromagnetic waves carry energy?

Example 16

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An EM wave has period T=1×10−8 sT = 1\times10^{-8}\,\text{s}. Find its wavelength.

Example 17

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An electromagnetic wave has a frequency of 6×1014 Hz6 \times 10^{14} \text{ Hz}. What is its wavelength? What type of EM radiation is this? Use c=3×108 m/sc = 3 \times 10^8 \text{ m/s}.

Example 18

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A pulse echoes off a wall in 4 μs4\,\mu\text{s} in air (cc accurate). How far is the wall?

Example 19

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Are the electric and magnetic fields in an EM wave in phase or 90∘90^\circ out of phase?

Example 20

challenge
A laser beam in vacuum has intensity I=1000 W/m2I = 1000\,\text{W/m}^2. Find the peak electric field E0E_0 (use I=12ϵ0cE02I = \tfrac{1}{2}\epsilon_0 c E_0^2, ϵ0c≈2.654×10−3 S/m\epsilon_0 c \approx 2.654\times10^{-3}\,\text{S/m}).
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