Practice Speed of Light in Physics

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

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Quick Recap

The speed of light is the speed at which electromagnetic waves travel in a vacuum. It is one of the most important constants in physics.

Light moves incredibly fast, but not infinitely fast.

Showing a random 20 of 50 problems.

Example 1

medium

How long does a signal take to travel

36000\text{ km}

to a geostationary satellite (one-way)?

Example 2

easy

Light travels through a vacuum. What is its speed?

Example 3

easy

In vacuum, do red light and blue light travel at the same speed?

Example 4

medium

Blue light has vacuum wavelength

\lambda_0 = 450\text{ nm}

. Find its wavelength in glass with

n = 1.52

Example 5

medium

Compare light speed in vacuum vs. diamond (

n = 2.42

). Find the speed ratio.

Example 6

easy

Green light has wavelength

\lambda = 5.0 \times 10^{-7} \text{ m}

in vacuum. Find its frequency.

Example 7

challenge

An observer measures light from a fast-moving spaceship's headlight. The ship moves at

0.5c

toward the observer. What speed does the observer measure for the light?

Example 8

medium

A pulse must travel

500\text{ m}

through a fiber with

n = 1.45

. Find the travel time.

Example 9

challenge

A pulse must travel 300 m through air (

n\approx1

) then 200 m through glass (

n=1.5

). Find the total time. Use

c=3.0\times10^8 \text{ m/s}

Example 10

hard

Light slowed to

v = 1.5\times10^8\text{ m/s}

in a medium has the same vacuum wavelength of

600\text{ nm}

. Find the wavelength in the medium.

Example 11

easy

Light from the Moon takes about

1.28\text{ s}

to reach Earth. Find the Earth-Moon distance.

Example 12

hard

Earth's circumference is about

4.0\times10^7\text{ m}

. How many times can light circle Earth per second (in vacuum)?

Example 13

medium

A green laser has vacuum wavelength

532\text{ nm}

. Find its frequency.

Example 14

easy

Fill in the blank: in vacuum, X-rays travel at ____ m/s.

Example 15

easy

Is the speed of light in vacuum the same for all observers?

Example 16

challenge

A round-trip light-pulse experiment over

2L = 600\text{ m}

in air gives

t = 2.00\times10^{-6}\text{ s}

. From this, estimate

c

Example 17

medium

A signal travels

1.5\text{ AU}

between Earth and Mars (closest approach). Time in minutes?

Example 18

medium

Which has higher frequency in vacuum: red light or blue light?

Example 19

easy

How long does light take to travel

3.0 \times 10^8 \text{ m}

in vacuum?

Example 20

easy

A laser pulse travels through vacuum for

5.0\times10^{-9}\text{ s}

. How far does it go? Use

c = 3.00\times10^8\text{ m/s}

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Related Concepts

Electromagnetic Waves Wave Speed Visible Light Special Relativity