Reflection & RefractionEdexcel IGCSE Physics: Flashcards

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State the law of reflection.

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State the law of reflection.: The angle of incidence equals the angle of reflection, both measured from the normal.
What is the normal, in the context of reflection and refraction?: An imaginary line drawn at 90° to a surface at the point where a light ray meets it.
Define refraction.: The change in direction and speed of a wave as it passes from one medium to another of different density.
What happens to light as it enters a denser medium (e.g. air to glass)?: It slows down and bends towards the normal.
What happens to light as it leaves a denser medium (e.g. glass to air)?: It speeds up and bends away from the normal.
What happens to light that travels exactly along the normal into a new medium?: It changes speed but does not change direction.
Give the equation for refractive index.: n = sin i / sin r, where i is the angle of incidence and r is the angle of refraction.
Define the critical angle.: The angle of incidence in a denser medium above which total internal reflection occurs instead of refraction.
What is total internal reflection?: When light travelling from a denser to a less dense medium strikes the boundary above the critical angle, so all the light is reflected back with none refracted out.
Give the equation linking critical angle and refractive index.: sin c = 1/n
Name two practical uses of total internal reflection.: Optical fibres (transmitting information/light along their length) and prisms (e.g. in periscopes and binoculars).
Why do optical fibres transmit light with very little loss?: Because light undergoes repeated total internal reflection off the walls of the fibre, keeping it trapped inside as it travels along the fibre's length.
What type of wave is light, and what can it do at a boundary?: Light is a transverse wave that can be reflected and refracted.