Investigating refraction through a prism

In a nutshell

By using a ray box and prism, you will investigate how light is refracted. You will do this by varying the angle of incidence and measuring the angles of refraction inside the prism.

Equipment list

The following equipment list can be used to conduct the experiment to investigate refraction in a prism.

Equipment	Use
Ray box and single slit grating	To create a narrow beam of light.
Prism	To refract 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	$Angle\ of\ refraction$
Control Variables	$Prism,\ prism\ placement,\ ray\ box$

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 refraction through a prism

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

1.	Set up the apparatus as shown in the diagram. The prism should be placed on top of the sheet of paper.
2.	Draw pencil lines around the edge of the prism. This means it can be placed back if anything goes wrong.
3.	Switch the ray box on and direct the light ray at the side of the block.
4.	Using the protractor, draw a line at $90\degree$ to the surface of the prism, where the light ray hits it. This is the normal. Draw another normal at the point that the light ray exits the prism.
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 surface of the prism (this should be where you have drawn the normal). The point the ray exits the prism. A point on the ray at a distance from the prism.
7.	Remove the block and, using a ruler, join up these lines to trace the outline of the light ray.
8.	Measure the angles of incidence and refraction (inside the prism) using a protractor.
9.	Replace the prism and repeat steps 5-7 with several more angles of incidence. The angle of incidence should all be kept between $0\degree$ and $70\degree$ and changed by a regular interval each time.

Analysis

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

1.	Compare the angles of incidence, $i$ , and refraction, $r$ , for the two boundaries for each light ray.
2.	Compare these to known theory. The light ray slows down when entering an optically more dense medium (air to a prism) so the angle of refraction should be smaller than the angle of incidence.
3.	Plot a graph of $\sin({r})$ against $\sin({i})$ . Draw a line of best fit for the graph.

Conclusion

Your results of your analysis should show that the measured experimental data matches with the theory of refraction. This means that the light ray bends towards from the normal when it enters an optically more dense medium (the prism).

Physics; Physics practicals; KS4 Year 10; Investigating refraction through a prism

The results from the graph should show a linear relationship between the $\sin({i})$ and $\sin({r})$ .

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.