Science and Technology K–6 · Year 5

Angle in equals angle out: the law of reflection on paper

Science understanding: Physical sciences

Practical, model not builtLow risk

This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.

The idea

Light bounces off a flat mirror so that the angle it bounces off at equals the angle it arrived at, measured from a line at right angles to the mirror, which a torch beam and a protractor show directly.

What you need

a small flat mirror (plastic safety mirror) stood upright with plasticine
a torch with a slit mask (a card with a 2 mm slot taped over the lens) to make a narrow beam
A3 paper, ruler, protractor, pencil
a darkened room

How to do it

Draw a straight line on the paper and stand the mirror along it. Draw the normal, a line at right angles to the mirror at its middle.
Shine the narrow beam along the paper at the middle of the mirror at 30 degrees from the normal. Mark two points on the incoming beam and two on the reflected beam.
Remove the torch, join the marks with the ruler and measure both angles from the normal with the protractor. Record them.
Repeat at 45 degrees and 60 degrees.
Set two mirrors at right angles to each other and send a beam in at any angle; trace its path.
Tabulate angle in against angle out and write the rule.

What you should see

Angle out equals angle in within the 1 to 2 degrees a protractor allows: 30 gives 30, 45 gives 45, 60 gives 60. Two mirrors at right angles send the beam back parallel to the way it came whatever the entry angle, because the two reflections add to 180 degrees of turning. Crumpled foil scatters the beam in many directions because its surface is rough, so it shows no clear image. A smooth curved mirror, such as the back of a spoon or a car's side mirror, still gives a clear image, only larger or smaller than the object, because the rule holds at every point of any smooth mirror.

What changes

What you change: angle of incidence
What you measure: angle of reflection
What you keep the same: same mirror
beam aimed at the mirror centre
angles measured from the normal

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Light bounces off a mirror at any angle.
Angles are measured from the mirror surface (they are measured from the normal, which is what the law uses).
Rough surfaces do not reflect (they reflect in every direction, so no image forms).

Safety card

Low riskLearners carry it out

Hazards

torch in eyes
glass mirror edges

Controls

plastic mirrors
beam kept on the paper

Note

Risk assessment before the lesson using Primary RiskAssess or the school's own template.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science and Technology K-6 Syllabus (2017), current, taught until 2026; a Stage 2 outcome, because NSW teaches the behaviour of light in Stage 2 ('investigate the behaviour of light', with reflection in a mirror and shadows as its examples), and neither the 2017 nor the 2024 Stage 3 content includes it; code read from the syllabus document on 22 September 2026ST2-8PW-ST
Science and Technology K-6 Syllabus (2017), current, taught until 2026; code read from the syllabus document on 22 September 2026ST3-1WS-S
Science and Technology K-6 Syllabus (2024), implemented from 2027; NESA's timeline is 2026 plan and prepare and 2027 start teaching, and schools may choose to implement it during 2026; code read from the outcomes page on 22 September 2026ST3-DAT-01
Australian Curriculum v9AC9S5U03AC9S5I03AC9S5I04

Sources

The pages the author read to write this activity.

All Concept Studio activities