Practice Diffraction 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 spreading of a wave as it passes through a gap or around the edge of an obstacle.

Waves 'bend around corners'—you can hear someone even if you can't see them.

Showing a random 20 of 50 problems.

Example 1

easy
What is diffraction?

Example 2

medium
Diffraction and refraction both change a wave's path. Which one requires a change of medium?

Example 3

easy
Diffraction changes a wave's direction of spread. Does it change the wave's frequency?

Example 4

easy
Do sound waves diffract, or only light?

Example 5

easy
Does the wave's speed change when it diffracts through a gap (same medium on both sides)?

Example 6

challenge
A single slit of width a=0.1a = 0.1 mm is lit with light of wavelength 500500 nm. Estimate the half-angle to the first diffraction minimum using sin⁡θ=λ/a\sin\theta = \lambda/a.

Example 7

medium
Red (λ=700\lambda = 700 nm) and blue (λ=450\lambda = 450 nm) light pass through the same slit. Which color shows the wider diffraction pattern, and by what ratio do the first-minimum angles compare for small angles?

Example 8

hard
A diffraction grating has 500 lines/mm500 \text{ lines/mm}. Light of wavelength 650 nm650 \text{ nm} passes through it. At what angle does the second-order maximum appear?

Example 9

medium
A WiFi router emits at λ=0.12\lambda = 0.12 m. Estimate the spreading angle when waves pass through a doorway of width a=0.9a = 0.9 m using sin⁡θ≈λ/a\sin\theta \approx \lambda/a.

Example 10

medium
Through a single slit of width aa, the first diffraction minimum is at angle θ1\theta_1 such that sin⁡θ1=λ/a\sin\theta_1 = \lambda/a. If you halve the slit width, what happens to θ1\theta_1 (assume small angle)?

Example 11

medium
If you double the slit width while keeping wavelength fixed, does the diffraction spreading increase or decrease?

Example 12

easy
Fill in the blank: diffraction is most noticeable when the gap size is approximately equal to the wave's ______.

Example 13

easy
Diffraction is strongest when the gap size is comparable to what wave property?

Example 14

hard
A grating has 600600 lines/mm. For green light λ=540\lambda = 540 nm, what is the highest order mm that produces a visible maximum (need sin⁡θ≤1\sin\theta \le 1)?

Example 15

easy
Why can you hear someone talking around a corner but not see them?

Example 16

hard
Two stars are separated by angular distance θ=1×10−6\theta = 1\times 10^{-6} rad. Can a telescope of aperture D=0.5D = 0.5 m at λ=550\lambda = 550 nm resolve them? Use θmin⁡=1.22λ/D\theta_{\min} = 1.22\lambda/D.

Example 17

easy
A sound wave of wavelength 0.70.7 m enters a doorway 0.80.8 m wide. Will the diffraction be significant?

Example 18

medium
A sound wave with f=440f = 440 Hz travels at v=340v = 340 m/s. Find its wavelength and decide whether it diffracts strongly through a 0.80.8 m wide doorway.

Example 19

hard
Sound at λ=0.5\lambda = 0.5 m diffracts around a building of width w=10w = 10 m. Estimate the angular spread θ≈λ/w\theta \approx \lambda/w in degrees.

Example 20

challenge
Two waves, both wavelength λ\lambda, pass through gaps of width λ\lambda and width 5λ5\lambda. The spreading angle scales roughly as λ/width\lambda/\text{width}. By what factor is the first gap's spreading larger?
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