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Shadow to order: position the source and screen

Year VIII pupils use PLA to draw an opaque screen on two feet and a torch sled. On a graduated track they position the torch and opaque screen to produce a requested shadow width on the projection screen by moving the opaque screen or source. They compare shadow edges with large and small sources and draw boundary rays in a top view.

Age
13–15 years
Length
approx. 45 min
Level
Medium
Where you teach
School
Purpose
Educational
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How to run this session

Stages and timing
  1. Opaque screen: frame and dense infill
  2. Feet and plate support
  3. Welds: the opaque screen stands
  4. First shadow
  5. Torch sled and small source
  6. Source at zero
  7. Orders A and B: move the opaque screen
  8. Order C: move only the source
  9. Boundary rays
  10. Optional: your order and penumbra

What gets built

A standing opaque screen and torch sled (the pair’s shadow kit), an observation sheet with three orders (distances and the ratio L : d), and three shadow diagrams with boundary rays at 1 : 2 scale.

What it practises
  • Explaining shadow changes through straight-line light propagation.
  • Predicting, measuring distances and comparing individual observations.
  • Drawing two boundary rays and recognising experimental limitations.

Success criteria
  • Each pupil records their own predictions, readings from three tests and conclusion in the six sheet rows.
  • Each pupil draws three diagrams at 1:2 scale, with two straight rays from the source through both screen ends to the projection screen, and compares them with observation.
  • The screen stands on cooled feet without transmitting light or rocking; the torch does not roll on the sled.

What you need
Filament
PLA
Colours
colour shown in the illustration
Also
3D pen (one per pupil), PLA filament (one colour per pupil, without changing the filament), transparent mat, pen stand, W1: full-size 1:1 PLA part templates (included printout, per pupil), T: graduated track 0-24 cm (included printout, per pair), E: projection screen sheet with frames and mask N to cut out (included printout, per pair), K: observation sheet (included printout, per pupil), broad-beam LED torch (1 per pair, additional classroom equipment approved in the plan; not modelled as geometry), book (1 per pair), pencil, ruler (per pupil), adhesive tape, scissors (per pair)

Files

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Version 45a6c26b-75c9-4d03-82bb-414be18d6923 Updated 2026-10-14

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