Physics Year 11 - Module 3 - Lesson 3

Wave Intensity and the Inverse Square Law

Use this worksheet after reading the lesson to practise the key ideas and prove you can meet the success criteria.

Name

Date

Class

1. Key Ideas

A sound or light source feels weaker as you move away from it, not because it runs out of energy instantly, but because the same energy is spread over a larger area. That spreading gives us the inverse square law.

The inverse square relationship $I \propto 1/r^2$
Why intensity falls with distance from a point source

2. Success Criteria

By the end, you should be able to:

The inverse square relationship $I \propto 1/r^2$
The ratio form $\dfrac{I_1}{I_2} = \dfrac{r_2^2}{r_1^2}$
The relationship $I \propto A^2$

3. Key Terms

WorkThe product of force and displacement in the direction of the force; W = Fd.

EnergyThe capacity to do work, measured in joules (J).

Kinetic EnergyThe energy of motion; KE = ½mv².

Potential EnergyStored energy due to position or configuration.

PowerThe rate at which work is done or energy is transferred; P = W/t.

Conservation of EnergyThe principle that energy cannot be created or destroyed, only transformed.

4. Activity: Build the Lesson Map

Use the lesson to complete the table. Keep answers brief but specific.

Prompt	Your answer
Main concept
Important example
Common mistake to avoid
How this links to the next lesson

5. Short Answer Questions

1. Explain this lesson goal in your own words: "The inverse square relationship $I \propto 1/r^2$". Use one specific example from the lesson.

Band 32 marks

2. Apply this idea to a new example: "The ratio form $\dfrac{I_1}{I_2} = \dfrac{r_2^2}{r_1^2}$". Show your reasoning clearly.

Band 43 marks

3. Analyse why this idea matters for understanding Wave Intensity and the Inverse Square Law: "The relationship $I \propto A^2$".

Band 54 marks

6. Extend: Apply the Idea

Band 5/65 marks

A student gives a memorised answer about Wave Intensity and the Inverse Square Law but does not use evidence or reasoning.

Improve the answer by writing a stronger response that uses accurate terminology, a relevant example and a clear explanation.

7. Multiple Choice

1. What is the best first step when answering a question about Wave Intensity and the Inverse Square Law?

A. Identify the key concept being tested

B. Write every fact from memory

C. Ignore the command word

D. Skip examples and evidence

2. Which answer would show stronger understanding of Wave Intensity and the Inverse Square Law?

A. An answer with accurate terms and reasoning

B. A copied definition only

C. A single-word response

D. An answer with no example

3. What should you do if a question asks you to explain?

A. Link the idea to a reason or cause

B. List unrelated facts

C. Only draw a diagram

D. Write the shortest possible answer

8. Success Criteria Proof

Finish with evidence that you can do each success criterion.

Success criterion 1

Prove that you can: The inverse square relationship $I \propto 1/r^2$