Refraction
 When light enters a glass block, it slows down, causing it to change direction
 When it leaves the block it speeds up again, changing direction once more
 As the light enters the block it bends towards the normal line
(Remember: Enters Towards)  When it leaves the block it bends away from the normal line
(Remember: Leaves Away)
Investigating Refraction
 In your examination you might be asked to write a method explaining how you might investigate the refraction of light through different shaped blocks
 As part of this method you should describe:
 What equipment you need
 How you will use the equipment
 How you will trace the rays of light before, while and after they pass through the block
Method:
 Place the glass block on a sheet of paper, and carefully draw around the block using a pencil
 Take a ray box and carefully aim the box so that a single ray of light passes through the block
 Using a pencil, mark some points along the path of the ray:
Before it reaches the block;
Where it hits the block;
Where it leaves the block;
After it has left the block  Now remove the block from the paper and, using a ruler and pencil, draw straight lines connecting points: a and b; b and c; c and d. The resulting line will show the path of the ray
 Replace the block within its outline and repeat the above process for a ray striking the block at a different angle
Exam Tip
Key things to remember include:

 Naming the apparatus that you need (remember the ray box)
 Explaining how to trace the rays
Snell's Law
 When light enters a denser medium (such as glass) it slows down and bends towards the normal
Diagram showing the angle of incidence, i, and the angle of refraction, r, of a ray of light entering a glass block
 Snell’s law gives the relationship between the angle of incidence i, and the angle of refraction r:
 Where n is the refractive index of the material
 You can rearrange this equation with the help of the formula triangle:
Use the formula triangle to help you rearrange the equation
 The refractive index is related to the speed of light in the material (which is less than its speed in a vacuum):
 The refractive index is a number that is always bigger than 1 and is different for different materials (n is about 1.5 for glass)
Exam Tip
Important: (sin i / sin r) is not the same as (i/r). Incorrectly cancelling the sin terms is a common mistake.
When calculating the value of i or r start by calculating the value of sin i or sin r.
You can then use the inverse sin function (sin^{1} on most calculators) to find the angle.