Science and Technology K–6 · Year 5

Light travels in straight lines: the three-card test

Science understanding: Physical sciences

PracticalLow risk

The idea

Light travels in straight lines, so a torch is seen through three holes only when the holes line up, and a shadow has the shape of the object that stops the light.

What you need

3 pieces of stiff card 15 x 15 cm, each with a 5 mm hole punched in the centre
3 lumps of plasticine to stand the cards
a torch
1 m of string
a darkened room

How to do it

Stand the three cards in a row 20 cm apart. Thread the string through all three holes and pull it taut to line them up. Remove the string.
Shine the torch through the first hole and look through the last: the torch is visible.
Move the middle card 2 cm sideways and look again. Record what you see.
Move it back and try bending the path with a mirror placed between cards 2 and 3 at 45 degrees, with the torch now shining from the side.
Hold a hand between the torch and a wall and describe the shadow's edge and shape.
Write a claim about the path light takes and the evidence from each step.

What you should see

The torch is seen only with all three holes on one straight line; a 2 cm shift of one card hides it completely. With a mirror the light reaches the third hole only by a new straight path from the mirror, at the angle the mirror sets. Shadows have the object's outline because light does not bend around the hand; the edge is slightly blurred because the torch face is not a single point.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

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

Light spreads around corners like sound does.
We see things because light comes out of our eyes.
A shadow is something dark that an object gives off.

Safety card

Low riskLearners carry it out

Hazards

dark room trip hazard

Controls

clear the floor
torch never shone into eyes

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
Australian Curriculum v9AC9S5U03AC9S5I01AC9S5I05

Sources

The pages the author read to write this activity.

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