Investigating reflection of light off a plane mirror

In a nutshell

By using a ray box and a plane mirror, you will investigate the law of reflection for light. You will do this by measuring the angle of incidence and reflection for a light wave reflecting off a plane mirror.

Equipment list

The following equipment list can be used to conduct the experiment to investigate reflection by a plane mirror.

Equipment	Use
Ray box and single slit grating	To create a narrow beam of light.
Power supply	To provide power for the ray box.
Plane mirror	To reflect the light ray.
Paper	To show the direction of the light ray.
Pencil	To mark the direction of the light ray.
Ruler	To ensure the lines of the light ray are drawn straight.
Protractor	To measure the angles of the light ray.

Experimental variables

The independent variable is the variable you change. The dependent variable is the variable that changes depending on the other variables, and is the one you measure. The control variables are the variables that are kept constant.

Independent Variable	$Angle\ of\ incidence$
Dependent Variable	$Angles\ of\ reflection$
Control Variables	$Ray\ box,\ plane\ mirror\ position\ and\ angle$

Safety precautions

When performing experiments, it is very important to consider safety precautions. This is so that no one gets hurt or injured during the experiment.

Hazard	Risk	Safety Measure
Ray box	The box gets very hot and could result in a burn.	Do not touch during use or straight after use. Leave it to cool before putting it away. If burnt, run burns under cold water.
Light ray	Looking into the light may damage eyes.	Don't look directly at the light. Keep the ray box directed away from you.
Dark room	There may be trip hazards that are difficult to see due to the lack of light	Take care when moving about, and try to limit movement. Check for hazards before dimming lights.

Method

These are the instructions to complete the experiment. Record all measurements taken as you work through the experiment in a table.

Physics; Physics practicals; KS4 Year 10; Investigating reflection of light off a plane mirror

1.	Power supply
2.	Ray box
3.	Ruler
4.	Mirror
5.	Protractor
6.	Paper
7.	Reflected ray

1.	Set up the apparatus as shown in the diagram. The mirror should be placed on top of the sheet of paper.
2.	Draw pencil lines around the edge of the mirror. This means it can be placed back if anything goes wrong.
3.	Switch the ray box on and direct the light ray at the mirror.
4.	Using the protractor, draw a line at $90\degree$ to the mirror's surface, where the light ray hits it. This is the normal.
5.	Position the ray box so that it makes an angle with the normal (angle of incidence).
6.	Mark on the paper: A point on the ray close to the box. The point the ray hits the mirror (where you have drawn the normal). A point on the reflected ray at a distance from the mirror.
7.	Remove the mirror and, using a ruler, join up these lines to trace the outline of the light ray.
8.	Measure the angles of incidence and reflection using a protractor.
9.	Repeat steps 5-8 for at least two more angles of incidence.

Analysis

This is how you will use the data recorded to form conclusions.

1.	Compare the angles of incidence and reflection.
2.	Compare these to known theory (the law of reflection). The angle of incidence and reflection should be the same for all angles of incidence.

Conclusion

The results from your experiment should confirm the law of reflection. This would mean the angle of incidence and reflection should be the same for all angles of incidence.

Evaluation

Once you have completed your experiment, it is important to consider how it could be improved. You should come up with ways to improve the accuracy of your values. If you got a result that seems unreasonable, think about why this was.