Lesson 3.3.2.1

3.3.2.1 Interference Quiz: AQA Physics, Unit 3

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.3.2.1, Interference: 20 multiple choice questions for the AQA Physics (7408), Unit 3: Waves, written with Revision Ninja.

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The 20 questions

  1. What does it mean for two sources to be coherent?

    • They have the same frequency and a constant phase difference
    • They have different frequencies
    • They are of equal amplitude only
    • They are located at the same point

  2. What path difference gives constructive interference?

    • a quarter wavelength
    • half-integer numbers of wavelengths
    • a whole number of wavelengths, n λ
    • zero always

  3. What path difference gives destructive interference?

    • n λ
    • (n + 1/2) λ
    • λ/4 exactly
    • 2 n λ only

  4. What is the formula for fringe spacing in Young's double-slit experiment?

    • w = λs/D
    • w = λ/(Ds)
    • w = λD/s
    • w = Ds/λ

  5. What does monochromatic light mean?

    • Light of zero frequency
    • Light from a single point
    • Light of many colours
    • Light of a single wavelength

  6. Why is the central fringe white when white light is used?

    • White light has no wavelength
    • Only white light is diffracted
    • Other colours are absorbed at the centre
    • All wavelengths add constructively at zero path difference

  7. Why are lasers commonly used in interference experiments?

    • They produce white light
    • They have no frequency
    • They are monochromatic and coherent
    • They are very cheap

  8. Light of wavelength 600 nm passes through slits 0.30 mm apart, with a screen 1.5 m away. What is the fringe spacing?

    • 0.03 mm
    • 30 mm
    • 0.3 mm
    • 3.0 mm

  9. Fringes separated by 2.0 mm are seen on a screen 2.0 m away from slits 0.4 mm apart. What is the wavelength?

    • 40 nm
    • 0.4 nm
    • 4 μm
    • 400 nm

  10. If the slit separation is doubled, what happens to the fringe spacing?

    • It quadruples
    • It halves
    • It doubles
    • It is unchanged

  11. If the screen is moved further from the slits, what happens to the fringe spacing?

    • It increases
    • It decreases
    • It is unchanged
    • It becomes zero

  12. Two sources emit in phase and the path difference is 1.5 λ. What is observed?

    • A pattern with equal brightness everywhere
    • Constructive interference, a maximum
    • Diffraction with no minimum
    • Destructive interference, a minimum

  13. Two sources emit in phase and the path difference is 2 λ. What is observed?

    • Destructive interference, a minimum
    • Partial interference with no pattern
    • Constructive interference, a maximum
    • No interference

  14. Loudspeakers emit 680 Hz sound in phase at a speed of 340 m/s. At a point the path difference is 0.25 m. What is observed?

    • Destructive interference, a minimum
    • A louder sound with no pattern
    • Constructive interference, a maximum
    • A sound at double frequency

  15. Microwaves of wavelength 3.0 cm arrive with path difference 6.0 cm. What is observed?

    • No change in intensity
    • Diffraction only
    • Destructive interference, a minimum
    • Constructive interference, a maximum

  16. Why do diffraction gratings produce spectral orders?

    • Light speeds up in the grating
    • Constructive interference occurs at angles that depend on wavelength
    • Each colour has a different charge
    • Gratings absorb all colours except one

  17. A double slit with spacing 1.0 mm gives fringe spacing 0.50 mm on a screen at 1.0 m. What is the wavelength?

    • 125 nm
    • 250 nm
    • 500 nm
    • 1.25 μm

  18. Why must a student take care when using lasers in interference experiments?

    • A laser beam can cause permanent damage to the eye
    • Lasers are too weak to be seen
    • Lasers always produce white light
    • Lasers have zero frequency

  19. If the wavelength of the light is increased while s and D stay the same, what happens to the fringe pattern?

    • The fringes spread further apart
    • The fringes disappear
    • The fringes become white
    • The fringes become closer together

  20. Why must two sources be coherent to produce a stable interference pattern?

    • So that they have different amplitudes
    • So that they emit white light
    • So that their phase difference is constant and the pattern does not move
    • So that they are in different places

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