# Required practical

## Investigate the reflection of light by different types of surface and the refraction of light by different substances

### Aim of the experiment

To investigate the reflection of light by different types of surface, and the refraction of light by different substances.

### Method

1. Set up a ray box, slit and lens so that a narrow ray of light is produced.
2. Place a 30 centimetre (cm) ruler near the middle of a piece of plain A3 paper. Draw a straight line parallel to its longer sides. Use a protractor to draw a second line at right angles to this line. Label this line with an ‘N’ for ‘normal’.
3. Place the longest side of a rectangular block against the first line. With the normal near the middle of the block, carefully draw around the block without moving it.
4. Use the ray box to shine a ray of light at the point where the normal meets the block. This is the .
5. The angle between the normal and the incident ray is called the . Move the ray box or paper to change the angle of incidence. The aim is to see a clear ray reflected from the surface of the block and another clear ray leaving the opposite face of the block.
6. Using a pencil on the paper, mark the path of:
• the incident ray with a cross
• the with a cross
• the ray that leaves the block with two crosses - one near the block and the other further away
7. Remove the block. Join the crosses to show the paths of the light rays.
8. Repeat steps 2 to 7 for a rectangular glass block.
9. Measure the angle of incidence, angle of refraction and angle of reflection for each block.

### Results

Record results in a suitable table.

The results for a polymer block:

Angle of incidence (°)Angle of reflection (°)Angle of refraction (°)
.........
.........

The results for a glass block:

Angle of incidence (°)Angle of reflection (°)Angle of refraction (°)
.........
.........

### Analysis

1. compare the angle of incidence with the angle of reflection for each block
2. compare the angle of incidence with the angle of refraction for each block

### Evaluation

The light rays should obey the law of reflection. To what extent do the results show this?

### Risks/hazards

HazardConsequenceControl measures
Ray box gets hotMinor burnsDo not touch bulb and allow time to cool
Semi-dark environmentIncreased trip hazardEnsure environment is clear of potential trip hazards before lowering lights
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