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Investigating refraction through a prism

Investigating refraction through a prism

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Explainer Video

Tutor: Madeleine

Summary

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 incidenceAngle\ of\ incidenceAngle of incidence​​
Dependent Variable
​Angle of refractionAngle\ of\ refractionAngle of refraction​​
Control Variables
​Prism, prism placement, ray boxPrism,\ prism\ placement,\ ray\ boxPrism, 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°90\degree90°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°0\degree0°and 70°70\degree70°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, iii, and refraction, rrr, 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)\sin({r})sin(r)​ against sin⁡(i)\sin({i})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)\sin({i})sin(i) and sin⁡(r)\sin({r})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. 

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Learn with Basics

Learn the basics with theory units and practise what you learned with exercise sets!
Length:
How we see

Unit 1

How we see

Light transmission and ray diagrams

Unit 2

Light transmission and ray diagrams

Jump Ahead

Score 80% to jump directly to the final unit.

Optional

Investigating refraction through a prism

Unit 3

Investigating refraction through a prism

Final Test

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FAQs - Frequently Asked Questions

How do you draw a normal?

Using the protractor, draw a line at 90° to the surface of the glass block, where the light ray hits it. This is the normal.

How does light refract when entering a optically more dense material?

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.

How do you do a refraction experiment?

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

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