• Quick retrieval from earlier learning (Static electricity and charges; Newton's law of gravitation and field strength). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. An object with a − charge is brought near an object with a − charge. Do they attract or repel? (attract / repel) → repelPrompt: Like charges repel; opposite charges attract.
2. The distance between two masses is multiplied by 4. By what factor does the gravitational force between them change? (F = G m₁ m₂ ÷ r²; give 4 decimal places if needed) → 0.0625Prompt: Force is proportional to each mass.
3. What causes lightning? (Magnets in the clouds / Thunder heating the air / The Sun's light / A huge build-up of static charge in clouds discharging) → A huge build-up of static charge in clouds dischargingPrompt: It is like a giant spark.

• Show a circuit with a gap and ask why the bulb doesn't light.
• Share the objective: Coulomb's law: force between charges. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Two small charged spheres carry 3 µC and 2 µC and are 0.5 m apart. What is the size of the force between them, in N? (F = k q₁ q₂ ÷ r², k = 8.99 × 10⁹ N m²/C², 1 µC = 10⁻⁶ C; give 2 decimal places)
• Step 1: F = 8.99 × 10⁹ × 3 × 10⁻⁶ × 2 × 10⁻⁶ ÷ 0.5² = 0.216
• Step 2: So the answer is: 0.22 N
• Answer: 0.22 N
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. Two small charged spheres carry 3 µC and 1 µC and are 0.5 m apart. What is the size of the force between them, in N? (F = k q₁ q₂ ÷ r², k = 8.99 × 10⁹ N m²/C², 1 µC = 10⁻⁶ C; give 2 decimal places) → 0.11 NPrompt: Convert µC to C.
2. Both charges are multiplied by 2 and the distance is unchanged. By what factor does the force change? → 4Prompt: F ∝ q₁ q₂ ÷ r²

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. Why don't we notice electrostatic forces between everyday objects most of the time? (Most objects are electrically neutral, with equal positive and negative charge / Electrostatic forces are very weak / They only act in space / Air blocks them) → Most objects are electrically neutral, with equal positive and negative chargePrompt: The force is huge compared with gravity, so why is it hidden?
2. Both charges are multiplied by 3 and the distance is unchanged. By what factor does the force change? → 9Prompt: F ∝ q₁ q₂ ÷ r²

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-12.