Lesson 3.3.2.3

3.3.2.3 Refraction at a plane surface Quiz: AQA Physics, Unit 3

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.3.2.3, Refraction at a plane surface: 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 is the refractive index of a substance?

    • The angle of incidence divided by the angle of refraction
    • The wavelength of light in the substance
    • The ratio of the speed in the substance to the speed in a vacuum
    • The ratio of the speed of light in a vacuum to the speed of light in the substance

  2. Which is Snell's law of refraction?

    • n1 cos(theta1) = n2 cos(theta2)
    • n1 sin(theta1) = n2 sin(theta2)
    • n1 sin(theta2) = n2 sin(theta1)
    • sin(theta1) = n1 n2

  3. What conditions are needed for total internal reflection?

    • Light travels from a higher to a lower refractive index and the angle exceeds the critical angle
    • Light travels from a lower to a higher refractive index at any angle
    • Light is always reflected at a boundary whatever the angle
    • Light travels from air to glass at any angle

  4. What is the formula for the critical angle?

    • tan(theta_c) = n1/n2
    • sin(theta_c) = n2/n1
    • sin(theta_c) = n1/n2
    • cos(theta_c) = n2/n1

  5. What is the function of cladding in an optical fibre?

    • It changes the wavelength of the light
    • It increases the speed of light in the core
    • It absorbs all light that reaches it
    • It has a lower refractive index so that total internal reflection occurs at the core boundary

  6. What causes modal dispersion in a step-index optical fibre?

    • The light speeds up in the cladding
    • The light has a range of wavelengths
    • Rays take different paths through the fibre and arrive at different times
    • The fibre absorbs the light unevenly

  7. What is the speed of light in glass of refractive index 1.5?

    • 1.5 × 10^8 m/s
    • 2.0 × 10^8 m/s
    • 4.5 × 10^8 m/s
    • 3.0 × 10^8 m/s

  8. Light travels from air (n = 1) into glass (n = 1.5) at 30 degrees to the normal. What is the angle of refraction?

    • 45 degrees
    • 19.5 degrees
    • 30 degrees
    • 14.5 degrees

  9. What is the critical angle for light from glass (n = 1.5) to air?

    • 41.8 degrees
    • 48.2 degrees
    • 60.0 degrees
    • 33.7 degrees

  10. What is the critical angle for light from water (n = 1.33) to air?

    • 48.8 degrees
    • 60.0 degrees
    • 36.9 degrees
    • 41.8 degrees

  11. Light travels from water (n = 1.33) to air at 30 degrees to the normal. What is the angle of refraction in air?

    • 19.5 degrees
    • 30 degrees
    • 41.7 degrees
    • 48.8 degrees

  12. A fibre core has refractive index 1.50 and cladding index 1.46. What is the critical angle at the core-cladding boundary?

    • 13.3 degrees
    • 86.7 degrees
    • 62.4 degrees
    • 76.7 degrees

  13. Light of wavelength 600 nm in vacuum enters glass of refractive index 1.5. What is its wavelength in the glass?

    • 300 nm
    • 900 nm
    • 400 nm
    • 600 nm

  14. When light enters glass from air, which quantity stays the same?

    • speed
    • frequency
    • wavelength
    • wave speed

  15. Light passes from air into a material at incidence 50 degrees and refracts at 30 degrees. What is the refractive index of the material?

    • 0.65
    • 2.05
    • 1.00
    • 1.53

  16. Why do pulses broaden as they travel along an optical fibre?

    • The light is reflected back to the source
    • The light is refracted into the cladding
    • Modal dispersion, because different paths take different times
    • The fibre expands in length

  17. Why does absorption reduce the amplitude of a pulse in an optical fibre?

    • The pulse is refracted out of the core
    • The wavelength is increased
    • The frequency is halved
    • The energy of the signal is absorbed by the fibre material

  18. When a ray meets a boundary at the critical angle, where does the refracted ray travel?

    • Reflected at 180 degrees
    • Along the boundary surface
    • Into the less dense medium at 90 degrees
    • Back into the denser medium

  19. A ray enters glass from air at normal incidence. What happens?

    • It bends towards the normal
    • It is totally reflected
    • It bends away from the normal
    • It is not deviated and continues in the same direction

  20. Light in a material of refractive index 1.6 meets an air boundary at 35 degrees. Does total internal reflection occur?

    • No, because 35 degrees is less than the critical angle of 38.7 degrees
    • Yes, because 35 degrees exceeds 38.7 degrees
    • No, because 35 degrees exceeds 38.7 degrees
    • Yes, because 35 degrees is less than 38.7 degrees

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