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. How is the refractive index n of a substance calculated from light speeds?

    • c times v
    • c minus v
    • v divided by c
    • c divided by v

  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. Which angle of incidence is required for total internal reflection to occur?

    • Greater than critical
    • Less than critical
    • Exactly forty-five degrees
    • Equal to zero

  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. How does optical fibre cladding refractive index compare to core refractive index?

    • It is zero
    • It is higher
    • It is equal
    • It is lower

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

    • Core diameter changes
    • Different wave speeds
    • Different path lengths
    • Light energy absorption

  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. Which effect causes light pulses to spread out in time along an optical fibre?

    • Material absorption
    • Total reflection
    • Modal dispersion
    • Core refraction

  17. What is the main effect of energy absorption in an optical fibre?

    • Increased pulse duration
    • Increased light speed
    • Reduced signal wavelength
    • Reduced pulse amplitude

  18. At what angle to the normal does a ray refract when incident at the critical angle?

    • 180 degrees
    • 90 degrees
    • 45 degrees
    • 0 degrees

  19. What happens to a light ray entering glass at normal incidence?

    • Total internal reflection
    • Refracts towards normal
    • Partial reflection only
    • No deviation

  20. Light in a medium of refractive index 1.6 meets air at 35°. Does total internal reflection occur?

    • No, light refracts
    • No, light disappears
    • Yes, light absorbs
    • Yes, light reflects

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