# 6.2.4 Refraction Ray Diagrams

### Refraction Ray Diagrams

• Refraction occurs when light passes a boundary between two different transparent media
• At the boundary, the rays of light undergo a change in direction
• The direction is taken as the angle from a hypothetical line called the normal
• This line is perpendicular to the surface of the boundaries and is usually represented by a straight dashed or dotted line
• The change in direction depends on which media the light rays pass between:
• From less dense to more dense (e.g air to glass), light bends towards the normal
• From more dense to less dense (e.g. glass to air), light bends away from the normal
• When passing along the normal (perpendicular) the light does not bend at all

How to construct a ray diagram showing the refraction of light as it passes through a rectangular block

• The change in direction occurs due to the change in speed when travelling in different substances
• When light passes into a denser substance the rays will slow down, hence they bend towards the normal
• The only properties that change during refraction are speed and wavelength – the frequency of waves does not change
• Different frequencies account for different colours of light (red has a low frequency, whilst blue has a high frequency)
• When light refracts, it does not change colour (think of a pencil in a glass of water), therefore, the frequency does not change

#### Worked Example

The diagram below shows two parallel rays of light entering and passing through prism A and prism C.

Draw a third parallel ray entering and passing through prism B.

Step 1: Draw a parallel ray on the left

Step 2: Draw the refracted ray at the first surface

• As the ray enters the block it bends towards the normal since it is going into a denser material
• In this case, the angle of refraction is smaller than the angle of incidence

Step 3: Draw the refracted ray at the second surface

• As the ray leaves the block it bends away from the normal
• In this case, the angle of refraction is larger than the angle of incidence

#### Exam Tip

Practice drawing refraction diagrams as much as you can! It’s very important to remember which way the light bends when it crosses a boundary:

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

### Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.
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