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Critical angle and total internal reflectionEdexcel International A Level Physics: Flashcards

What these 12 flashcards ask

  • What is total internal reflection?
  • State the two conditions for total internal reflection.
  • Define the critical angle.
  • Write the equation for the critical angle of a material in air.
  • Write the general equation for the critical angle at a boundary between media 1 and 2.
  • What happens when the angle of incidence equals the critical angle?
  • What happens when the angle of incidence is less than the critical angle?
  • Can total internal reflection occur when light goes from air into glass?
  • How does the critical angle change as the refractive index of a material increases?
  • Calculate the critical angle of glass with n = 1.50 in air.
  • How do you predict whether TIR occurs at an interface?
  • How do optical fibres carry light?

Exam questions on Critical angle and total internal reflection

  1. A ray of light travels inside a rectangular block of glass of refractive index 1.60 and strikes a flat glass–air boundary from inside the glass. Take the refractive index of air as 1.00.
    The block is now immersed in water of refractive index 1.33. Calculate the critical angle for the glass–water boundary.2 marks
  2. A bare optical fibre made of glass with refractive index 1.52 is surrounded by air. Light signals travel along the fibre by repeatedly meeting the side wall of the fibre, which is a glass–air boundary.
    A ray inside the fibre meets the side wall at an angle of incidence of 38°. Determine whether the ray is totally internally reflected.2 marks
  3. A small lamp is fixed at the bottom of a swimming pool, 2.0 m below the water surface, and shines light in all directions upwards. The refractive index of the water is 1.33 and that of air is 1.00. A swimmer looks at the surface from above.
    Calculate the critical angle for the water–air surface. Explain why light from the lamp that reaches the surface at an angle of incidence of 60° does not emerge into the air.3 marks
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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).