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 km36000\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 λ0=450 nm\lambda_0 = 450\text{ nm}. Find its wavelength in glass with n=1.52n = 1.52.

Example 5

medium
Compare light speed in vacuum vs. diamond (n=2.42n = 2.42). Find the speed ratio.

Example 6

easy
Green light has wavelength λ=5.0×10−7 m\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 0.5c0.5c toward the observer. What speed does the observer measure for the light?

Example 8

medium
A pulse must travel 500 m500\text{ m} through a fiber with n=1.45n = 1.45. Find the travel time.

Example 9

challenge
A pulse must travel 300 m through air (n≈1n\approx1) then 200 m through glass (n=1.5n=1.5). Find the total time. Use c=3.0×108 m/sc=3.0\times10^8 \text{ m/s}.

Example 10

hard
Light slowed to v=1.5×108 m/sv = 1.5\times10^8\text{ m/s} in a medium has the same vacuum wavelength of 600 nm600\text{ nm}. Find the wavelength in the medium.

Example 11

easy
Light from the Moon takes about 1.28 s1.28\text{ s} to reach Earth. Find the Earth-Moon distance.

Example 12

hard
Earth's circumference is about 4.0×107 m4.0\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 nm532\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 m2L = 600\text{ m} in air gives t=2.00×10−6 st = 2.00\times10^{-6}\text{ s}. From this, estimate cc.

Example 17

medium
A signal travels 1.5 AU1.5\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 3.0×108 m3.0 \times 10^8 \text{ m} in vacuum?

Example 20

easy
A laser pulse travels through vacuum for 5.0×10−9 s5.0\times10^{-9}\text{ s}. How far does it go? Use c=3.00×108 m/sc = 3.00\times10^8\text{ m/s}.
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