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

medium
How long does light take to travel 1 km in vacuum?

Example 2

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

Example 3

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

Example 4

hard
An EM wave travels through a material at v=1.5×108 m/s. Find the refractive index n.

Example 5

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A laser pulse travels 9×108 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 Hz. What is the wavelength of the microwaves? Use c=3×108 m/s.

Example 7

easy
An EM wave has frequency 5×109 Hz. Find its wavelength in vacuum.

Example 8

medium
A microwave has frequency f=3×109 Hz. Find its wavelength in vacuum (in cm).

Example 9

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An EM wave has frequency f=2×1014 Hz. What is its period?

Example 10

challenge
A pulsed EM source emits at f=1×109 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=1.5, an EM wave originally at λ=600 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 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/m. Find the magnetic field amplitude B0.

Example 15

easy
Do all electromagnetic waves carry energy?

Example 16

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An EM wave has period T=1×10−8 s. Find its wavelength.

Example 17

easy
An electromagnetic wave has a frequency of 6×1014 Hz. What is its wavelength? What type of EM radiation is this? Use c=3×108 m/s.

Example 18

medium
A pulse echoes off a wall in 4 μs in air (c 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∘ out of phase?

Example 20

challenge
A laser beam in vacuum has intensity I=1000 W/m2. Find the peak electric field E0 (use I=12ϵ0cE02, ϵ0c≈2.654×10−3 S/m).
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