Opening

BUILD · SCIENCE · Lesson 8 of 10

Same card. Two very different shadows.

Learning intention

Describe how moving an opaque card changes its shadow size when the source and screen stay fixed.

The card stays 4 cm high.

The source and screen stay still.

Can its shadow change size?

Success looks like

Name the changed distance and what stays fixed.
Use data to describe the shadow-size pattern.
Predict a suitable card position for a stated target.

Retrieval

BUILD · SCIENCE · Lesson 8 of 10

Keep the shadow idea clear

1. What does an opaque card do?

2. Where is the shadow seen?

3. Is the shadow a solid object?

I do

BUILD · SCIENCE · Lesson 8 of 10

I move the card near the source

The source and screen stay fixed.

The card is 20 cm from the source.

The same card blocks a wider spread.

Change the card position

Diagram description

Side-view light-ray model. Ray arrows point away from a small source. Boundary rays pass the top and bottom edges of an opaque card and locate the shadow on a screen.

I do

BUILD · SCIENCE · Lesson 8 of 10

I move it towards the screen

Now the card is 50 cm from the source.

Its size is unchanged.

The shadow on the screen is smaller.

Change the card position

Diagram description

Side-view light-ray model. Ray arrows point away from a small source. Boundary rays pass the top and bottom edges of an opaque card and locate the shadow on a screen.

I do

BUILD · SCIENCE · Lesson 8 of 10

I measure the same dimension

Measure bottom to top.

Use centimetres each time.

Keep the ruler beside the screen.

Measure one height in centimetres

Diagram description

Front-view screen with a rectangular shadow beside a ruler. The shadow runs from zero to eight centimetres; use the same top-to-bottom measure each time.

Continue within this stage’s shared time.

We do

BUILD · SCIENCE · Lesson 8 of 10

Find the pattern in the model

Go to interactive investigation

Compare the three positions.

Which gives the largest shadow?

Use two numbers as evidence.

Constructed ideal point-source model; source → screen = 100 cm
Source → card	Card height	Model shadow height
20 cm	4 cm	20 cm
40 cm	4 cm	10 cm
50 cm	4 cm	8 cm

W1. What changes as the card moves away from the source?

My response — say it, sketch on paper or type

Shadow-size studio: move the card

Ideal point-source model. Keep source and screen 100 cm apart and the same 4 cm-high card. Predict, test, explain.

Shadow-size model

Change source-to-object distance. The source and screen stay fixed. This is ideal point-source geometry, not practical measurements.

Source to object: cm

The object stays the same height. Ray lines show limiting paths from an ideal point source; this model omits the fuzzy edges of a real torch.

Decision 1 of 3

At 20 cm from the source, which model shadow height matches the evidence?

Choose, test, then explain together. Evidence diagrams appear only after your test. Diagram transitions explain the model; they do not represent real elapsed time. Use Pause model to stop transitions and model controls, or your device’s reduced-motion setting. The printed We do activity provides the paper route.

We do

BUILD · SCIENCE · Lesson 8 of 10

Meet the studio target

Target: a shadow 10 cm high.

Choose a card position.

Explain why the other positions miss.

W2. Which model position meets the target?

My response — say it, sketch on paper or type

Hinge

BUILD · SCIENCE · Lesson 8 of 10

Which prediction follows this setup?

The source and screen stay fixed.

Move the same card towards the source.

You do

BUILD · SCIENCE · Lesson 8 of 10

Choose your investigation route

Match the model values.

Recommend a studio position.

Predict between trials.

My response — say it, sketch on paper or type

You do

BUILD · SCIENCE · Lesson 8 of 10

Use the evidence

Read or point to one clue.

Record what it supports.

Keep your explanation short.

My response — say it, sketch on paper or type

Continue within this stage’s shared time.

You do

BUILD · SCIENCE · Lesson 8 of 10

Make your own science record

Complete your chosen route.

Use a diagram, words or speech.

Check one answer with the evidence.

My response — say it, sketch on paper or type

You do

BUILD · SCIENCE · Lesson 8 of 10

Check and improve

Does my answer match the evidence?

Have I explained why?

Improve one label or sentence.

My response — say it, sketch on paper or type

Continue within this stage’s shared time.

Review

BUILD · SCIENCE · Lesson 8 of 10

Lundy loop: improve our account

Choose how to share one idea.

Listen to another explanation.

Use evidence to improve our account.

What must we name when we say “nearer makes it larger”?

My response — say it, sketch on paper or type

Exit

BUILD · SCIENCE · Lesson 8 of 10

Three quick checks

E1. What happens to shadow size as this card moves towards the source?

E2. Name one thing kept fixed.

E3. Which model distance gives a 10 cm shadow?

My response — say it, sketch on paper or type

My science task sheets

Choose one route with your teacher. Shared evidence and the exit sheet appear in every route. Your work stays here while the page is open; save it before closing.

Evidence: studio model cards

Constructed ideal point-source model. Source and screen stay 100 cm apart. The same 4 cm-high card stays upright.

Card	Source → card distance	Model shadow height
A	20 cm	20 cm
B	40 cm	10 cm
C	50 cm	8 cm

These numbers are model predictions, not class measurements. Real LED results can differ because the source has size and edges may be blurred.

W1. Describe the pattern as source-to-card distance increases.W2. Choose A, B or C for a 10 cm shadow. Explain.Observation option: write a real distance and shadow height here. Label it “our measurement”.

Route 1 • Match and choose

Use the shared model table. Word bank: larger / smaller / source.

S1. Which card position gives the largest model shadow? A: 20 cm B: 40 cm C: 50 cm

S2. Copy the model shadow height at 50 cm.S3. In this setup, moving towards the source makes the shadow __.S4. Name two things kept the same.

S5. Which position gives the target 10 cm shadow? 20 cm 40 cm 50 cm

Route 2 • Record and recommend

Make a studio instruction from the model evidence.

Task	Source → card	Model shadow height
T1	20 cm
T1	40 cm
T1	50 cm

T2. Describe the pattern using two values.T3. Recommend a position for a 10 cm shadow. State the controls.T4. Explain why a real torch result might not match exactly.

Route 3 • Predict between the trials

The same model now places the card 30 cm from the source. Source and screen remain fixed.

X1. Predict whether its shadow is larger or smaller than the 40 cm-position shadow.X2. Use the table to give two bounds for the predicted height. No formula is needed.X3. Explain why the card itself has not grown.X4. A team moves both the card and screen. Can it use our pattern without checking the new setup? Explain.

Exit and reflection

Point, draw, write or tell an adult.

E1. What happens to shadow size as this card moves towards the source?E2. Name one thing kept fixed.E3. Which model distance gives a 10 cm shadow?R1. Which idea did you improve after hearing evidence?R2. What would you investigate or ask next?