1. 6
6.3.2 What are the laws of reflection?
We all know what we see when we look in a mirror – but why do we see
ourselves, and why is the mirror image so clear?
Equipment
• plain mirror • mirror holder
• light source that gives a single • A3 plain paper
ray
• angle measurer (protractor) • ruler
Safety
• Handle mirrors with care – if you break one you could cut yourself on
the broken pieces.
• Light sources can become hot enough to burn skin.
Obtaining evidence
1 Look at the image of a candle in a mirror. If you look
at the tiles on the floor, you can see that the candle
appears to be the same distance behind the mirror
as it is in front. mirror
2 Now look at the diagram that represents the situation as seen from above.
You will notice that light rays and angles have been given names.
mirror
reflected
angle of
light ray
reflection
normal
angle of
incidence
position of candle
image of candle incident
light ray
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2. 6
6.3.2 What are the laws of reflection?
3 You are going to do an experiment, using the equipment listed above,
to confirm or contradict the statement that ‘the angle of reflection is
equal to the angle of incidence’.
4 Use the angles shown in the diagram below for incident light.
80° 70°
60° incident light rays
50°
40°
30°
20°
10°
normal
mirror
5 Draw a results table to record you measurements in. This will need to
record the incident angle and the reflected angle
6 Draw the normal, the position of the mirror and the incident angles
accurately on a piece of paper. This should look very similar to the
diagram above. Put the mirror along the mirror line on the paper and
shine a light ray along one of the incident lines you have drawn. Draw
the path of the reflected ray on the paper. Repeat this for all of the
incident angles.
7 Now remove the mirror and measure the angle of each reflected ray
and record the results in your results table. Notice that the angles are
measured between the normal and the light ray.
Presenting the results
1 Plot a graph of your results and add a straight line of best fit.
Considering the evidence
1 Using your results, write a simple statement describing the link
between the angle of reflection and the angle of incidence.
Evaluating
2 How accurately do you think you measured the angles is? Give an
answer in numbers, for example plus or minus 5°.
Extension
3 A flat mirror gives an accurate reflection of your face. Describe what
would happen to your reflection if the mirror was not flat, for example if
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3. 6
6.3.2 What are the laws of reflection?
you looked at your reflection in water with ripples on it. You might like
to use sketches to help you.
4 Hold this piece of paper facing you. Notice the letter F (letter 1) below
is the right way up and the right way round. Now turn the paper over so
that the top edge of the paper is still at the top. Notice the reversed F
(letter 2), seen through the paper from the other side, now looks the
right way round. Turn the paper back towards you again. Now turn the
paper round so that the top of the paper is at the bottom. Now notice
the letter F (letter 3) that looks the right way round. Explain why the
different reversed versions of the F look right in the mirror depending
on what you did to the paper.
1 2
3
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This worksheet may have been altered from the original.