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What you need to know

Reflections and Exam tips



Refraction is the bending of light.

Refraction happens when light moves between two mediums that have a different density.

When light moves into a medium with a higher density, it slows down and will bend towards the normal.

When it moves into a less dense medium, it speeds up and bends away from the normal.

Relationships between angle of incidence and angle of refraction.

When the Sin of the angle of incidence is divided by Sin of the angle of refraction the answer will always be a constant.

The value of the constant will change depending on materials being used for refraction.

Refractive Index

The refractive index is a measure of how much light is refracted by a material when light passes through the material.

Refractive Index can be calculated by using the equation:

Refractive index = Sin I / Sin R

Where I = angle of incidence and R = angle of refraction.

Total Internal Reflection

Critical Angle

When a semi-circular block is used for refraction, as light leaves the semi-circular block it bends away from the normal.

This is because it is moving from a more dense to a less dense medium.

However, as the angle of incidence is increased, a point is reached where the refracted light seems to run across the top of the glass block. The angle at which this happens is called the critical angle.

When the angle is increased more the light ray is no longer refracted but appears to reflect off the inside of the straight edge of the semi-circular block. This is known as total internal reflection.

The critical angle of a material can be found using the following formula:

Refractive index = 1/sin(C)

Where Refractive index = property of a material and C = Critical angle.

Uses of total internal reflection

Fibre Optic cables - are used in high speed internet which involve sending light through one end in short bursts and this will light up the other end.

Endoscopes - are cameras that can be used to look inside patients without having to perform invasive surgery. Endoscopes involve light being shone into one end, travels through the endoscope, shines off the inside of a patient, back along the endoscope and to form a picture.