Visible Light Examples: 44 Problems with Answers

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Visible Light.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Physics.

Concept Recap

Visible light is the small part of the electromagnetic spectrum that human eyes can detect. Different wavelengths in this range are seen as different colors.

Visible light is just the slice of electromagnetic waves our eyes happen to notice.

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How to Use These Examples

Read the first worked example with the solution open so the structure is clear.
Try the practice problems before revealing each solution.
Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Visible Light starts by following rays or wavefronts through boundaries, materials, and image locations.

Common stuck point: Students often know a formula related to visible light but skip the recognition step: Am I tracking how light travels through space or materials, including boundary rules and image location when needed? That leads to a correct-looking substitution attached to the wrong physical model.

Sense of Study hint: Ask: Am I tracking how light travels through space or materials, including boundary rules and image location when needed?

Worked Examples

Example 1

medium

A red light with wavelength 650 nm in vacuum enters water (

n=1.33

). (a) Find its frequency. (b) Find its wavelength inside the water.

Answer

(a)\;f\approx 4.62\times 10^{14}\;\text{Hz};\;(b)\;\lambda_w\approx 489\;\text{nm}

First step

(a)

f = c/\lambda_0 = (3.0\times 10^8)/(650\times 10^{-9}) \approx 4.62\times 10^{14}\;\text{Hz}

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Example 2

medium

Sunlight (white) shines on a wall painted matte blue. (a) Which wavelengths reach an observer? (b) What does the wall look like under a pure red light?

Example 3

hard

A monochromatic green source (

\lambda_0 = 530\;\text{nm}

) enters a glass with

n_g = 1.52

for green. (a) Find

\lambda

in the glass. (b) If a red component at 650 nm enters the same glass with

n_r = 1.50

, find its wavelength in the glass. (c) Which color has the larger refractive index?

Example 4

challenge

A camera's image sensor pixel is illuminated by 600 nm light at

50\;\mu\text{W}/\text{m}^2

. The pixel area is

4\;\mu\text{m}\times 4\;\mu\text{m}

. Find the photon arrival rate at the pixel.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy

What part of the electromagnetic spectrum can human eyes detect?

Example 2

easy

Within visible light, which has the longer wavelength: red or violet?

Example 3

easy

White light is best described as what?

Example 4

easy

A red light source is made brighter without changing its color. Does its wavelength change?

Example 5

easy

Orange light has

\lambda = 600 \text{ nm}

. Express this wavelength in meters.

Example 6

easy

Which color of visible light carries the highest frequency: red, green, or violet?

Example 7

easy

Are infrared and ultraviolet waves visible to the human eye?

Example 8

easy

Green light has frequency

f = 6.0 \times 10^{14} \text{ Hz}

. Find its wavelength in vacuum.

Example 9

medium

A prism splits white light into colors. Why does this happen?

Example 10

medium

Blue light (

\lambda = 450 \text{ nm}

) enters water where

n=1.33

. Find its wavelength in water.

Example 11

medium

Two light sources have the same intensity but one is red and one is blue. Which delivers higher-energy photons?

Example 12

medium

Red light at 700 nm passes from vacuum into glass (

n=1.5

). Find its speed in the glass.

Example 13

medium

A leaf appears green in white light. Why?

Example 14

medium

Sunlight contains all visible wavelengths. After passing through a perfect red filter, what reaches the eye?

Example 15

challenge

In a vacuum, light A has wavelength 400 nm and light B has 600 nm. Find the ratio of their frequencies

f_A/f_B

Example 16

challenge

Violet (400 nm) and red (700 nm) light both enter glass where

n=1.50

. Assuming

n

is the same for both, by what factor does each wavelength shrink, and do their frequencies differ in glass?

Example 17

challenge

A photon of green light has frequency

6.0\times10^{14} \text{ Hz}

. Using

h = 6.63\times10^{-34} \text{ J}\cdot \text{s}

, find its energy.

Example 18

medium

Sunlight passes through a green filter then a red filter. What light emerges?

Example 19

medium

A 450 nm blue photon and a 650 nm red photon: which has the longer wavelength and lower frequency?

Example 20

medium

Yellow light has

\lambda = 580 \text{ nm}

in vacuum. Find its frequency.

Example 21

easy

Which color of visible light has the shortest wavelength?

Example 22

easy

Light with wavelength 520 nm appears what color?

Example 23

easy

True or false: increasing the brightness of a light bulb changes the wavelength of its red glow.

Example 24

easy

Light has frequency

f = 5.0\times 10^{14}\;\text{Hz}

in vacuum. Find its wavelength.

Example 25

easy

Is X-ray radiation part of visible light?

Example 26

easy

A red filter is held in front of a white light. What colors pass through?

Example 27

medium

A green light has

\lambda=550\;\text{nm}

in vacuum. Find its frequency in Hz.

Example 28

medium

A blue laser at 450 nm enters glass with

n=1.5

. Find its speed inside the glass.

Example 29

medium

In a vacuum, photon A has wavelength 400 nm and photon B has wavelength 800 nm. Find the ratio

E_A/E_B

of their energies.

Example 30

medium

A yellow filter and a blue filter are stacked. Which color passes through?

Example 31

medium

A prism disperses white light. Which color is bent the MOST as it enters the prism (typical crown glass)?

Example 32

medium

A light source emits photons of frequency

f=4.3\times 10^{14}\;\text{Hz}

. Use

h=6.63\times 10^{-34}\;\text{J s}

to find each photon's energy.

Example 33

medium

Two LEDs emit at 450 nm and 650 nm. Which has the higher photon energy, and by what factor?

Example 34

medium

A green light enters glass and slows from

c

2.0\times 10^8\;\text{m/s}

. Find the glass's refractive index for green light.

Example 35

hard

Light with vacuum wavelength 600 nm enters a transparent solid where its speed is

1.8\times 10^8\;\text{m/s}

. Find (a) the refractive index and (b) the wavelength inside the solid.

Example 36

hard

A monochromatic light source emits

1.0\;\text{W}

\lambda = 500\;\text{nm}

light. Use

E = hc/\lambda

to estimate the number of photons emitted per second.

Example 37

hard

A bee can see ultraviolet light at 350 nm; a human cannot. By what percentage shorter is the bee's UV than the human violet edge near 400 nm?

Example 38

hard

Sunlight intensity on Earth is about

1000\;\text{W/m}^2

, and about 40% is in the visible band. Estimate the visible-light power striking a

1.5\;\text{m}^2

solar panel.

Example 39

hard

A laser pointer emits at 532 nm with output power 5 mW. About how many photons per second does it emit?

Example 40

challenge

Two coherent visible-light beams overlap. Beam A has wavelength 500 nm and beam B has 700 nm. State whether they can produce stable, stationary interference fringes (assume both have the same direction and equal amplitude).

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Related Concepts

Electromagnetic Spectrum Speed of Light Mirrors Lenses

Background Knowledge

These ideas may be useful before you work through the harder examples.

electromagnetic spectrumspeed of light