• Quick retrieval from earlier learning (Current and voltage rules in series and parallel circuits; Current, voltage and resistance (V = IR)). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Two lamps are connected in series to a 9 V battery. The voltage across the first lamp is 2.25 V. What is the voltage across the second lamp, in V? → 6.75 VPrompt: In series, the supply voltage is shared between components.
2. A current of 4 A flows through a 6 Ω resistor. What is the potential difference (voltage) across it, in V? → 24 VPrompt: V = I × R
3. Two lamps are in parallel. The current through one branch is 1 A and through the other is 1.2 A. What current flows from the battery, in A? → 2.2 APrompt: In parallel, the current splits between branches.

• Show a circuit with a gap and ask why the bulb doesn't light.
• Share the objective: Total resistance of series and parallel networks. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Three resistors of 2 Ω, 15 Ω and 10 Ω are connected in series. What is the total resistance, in Ω?
• Step 1: 2 + 15 + 10 = 27
• Step 2: So the answer is: 27 Ω
• Answer: 27 Ω
• 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. Three resistors of 10 Ω, 6 Ω and 2 Ω are connected in series. What is the total resistance, in Ω? → 18 ΩPrompt: In series, resistances add.
2. A 12 Ω resistor and a 4 Ω resistor are connected in parallel. What is their combined resistance, in Ω? (1/R = 1/R₁ + 1/R₂) → 3 ΩPrompt: The total is less than the smallest resistor.

• 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. A 10 Ω resistor and a 15 Ω resistor are connected in parallel. What is their combined resistance, in Ω? (1/R = 1/R₁ + 1/R₂) → 6 ΩPrompt: The total is less than the smallest resistor.
2. A 8 Ω resistor is in series with a parallel pair of 10 Ω and 10 Ω. The supply is 6.5 V. What current flows from the supply, in A? → 0.5 APrompt: Find the parallel pair's resistance first.

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