Science and Technology K–6 · Years 1–2

Shadows with a torch: size changes with distance

Physical World, energy comes in different forms that can be detected (NSW 2017); Light and sound interact with materials in different ways (NSW 2024); Science inquiry (ACARA v9)

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

A shadow forms where an object stops light; moving the object closer to the light makes the shadow bigger.

What you need

A small torch with a wide beam, lying on its side on the floor 100 cm from a wall in a darkened room and pointing at the wall, so its bulb sits just above the floor, close to the level of the bottom of the figure (not a phone torch: lying flat its light points at the ceiling, and standing up its light sits well above the bottom of the figure)
A 10 cm cardboard figure standing on the floor; a 1 m tape on the floor from the torch to the wall
A ruler taped to the wall to read shadow height
Recording table: figure distance from the torch (cm), shadow height (cm)

How to do it

Place the figure 50 cm from the torch. Measure the shadow's height on the wall, reading to the middle of the soft edge.
Move the figure to 25 cm and then to 75 cm. Measure each time.
Predict the shadow height at 20 cm, then move the figure there and measure.
Hold a clear plastic sheet and then a tissue where the figure was and describe the shadow each makes.

What you should see

The closer the figure is to the torch, the bigger the shadow: at 50 cm the 10 cm figure casts a shadow of about 20 cm; at 25 cm about 40 cm; at 75 cm about 13 cm; at 20 cm about 50 cm (shadow height = figure height times wall distance divided by figure distance). These figures assume the bulb is level with the bottom of the figure; the higher the bulb sits above the floor, the shorter every shadow on the wall comes out, which is why the torch lies on its side on the floor. A real torch has a bulb of some width, so the shadow edge is soft; reading to the middle of the soft edge gives heights close to these values. Clear plastic makes almost no shadow; tissue makes a faint grey one. The learner knows it worked when the shadow at 25 cm is close to twice the shadow at 50 cm.

What changes

What you change: distance from the torch to the figure
What you measure: shadow height on the wall (cm)
What you keep the same: same torch position 100 cm from the wall, lying on its side with its bulb just above the floor
same figure
room darkened

Common misconceptions

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

A shadow is something the object gives off.
Shadows are always the same size as the object.

Safety card

Low riskLearners carry it out

Hazards

Tripping in a darkened room; torch shone into eyes

Controls

Floor cleared before the lights go down; torch left lying in place and pointed at the wall

Note

No chemicals or heat. Record the activity on the school's risk assessment (Primary School RiskAssess, Ecosolve Australia, riskassess.com.au).

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), NESA. Current syllabus; NESA's timeline is 2026 plan and prepare, 2027 start teaching the 2024 syllabus. Code read from the official syllabus document on 2026-09-23.ST1-8PW-S
Science and Technology K-6 Syllabus (2017), NESA. Current syllabus; NESA's timeline is 2026 plan and prepare, 2027 start teaching the 2024 syllabus. Code read from the official syllabus document on 2026-09-22.ST1-1WS-S
Science and Technology K-6 Syllabus (2024), NESA. Implementation from 2027, so this code describes the future syllabus. Code read from the outcomes page on 2026-09-22.ST1-SCI-01 ST1-PQU-01 ST1-DAT-01
Australian Curriculum v9AC9S1I01AC9S1I02AC9S1I03AC9S1I04

Sources

The pages the author read to write this activity.

All Concept Studio activities