Back to the lesson plan builder
Lesson length30 min45 min60 min
Questions🔀 New questions

Print the plan for yourself; the student sheet prints on its own page after it.

Science lesson plan · 12th grade (Year 13 in England) · 30 minutes

Total resistance of series and parallel networks

Electricity and magnetism

CCSS NGSS.HS-PS3-5England: GCSE Physics: Electricity (resistors in series and parallel)England: A level Physics: Electricity (extension)

Objective and success criteria

Students will: Total resistance of series and parallel networks.

  • I can answer questions on today's skill on my own, without help.
  • I can explain each step and say why it works.
  • I can check my answer and spot a mistake.

Before and after

Needs first: Current and voltage rules in series and parallel circuits; Current, voltage and resistance (V = IR)

Leads to: the next skill in this area.

Materials: Circuit kits (cells, wires, bulbs), Circuit symbol cards, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).

Warm-up · 4 min

  • 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 6 V. What is the voltage across the second lamp, in V? → 3 VPrompt: In series, the supply voltage is shared between components.
  2. A current of 4 A flows through a 12 Ω resistor. What is the potential difference (voltage) across it, in V? → 48 VPrompt: V = I × R
  3. A 1.9 A current leaves a battery and splits into two parallel branches. One branch carries 1.5 A. What current flows in the other branch, in A? → 0.4 APrompt: Current is not used up; it is shared between branches.

Hook · 3 min

  • 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.

I do: model it · 7 min

  • 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.

We do: guided practice · 6 min

  • 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 12 Ω, 6 Ω and 5 Ω are connected in series. What is the total resistance, in Ω? → 23 ΩPrompt: In series, resistances add.
  2. A 6 Ω resistor and a 12 Ω resistor are connected in parallel. What is their combined resistance, in Ω? (1/R = 1/R₁ + 1/R₂) → 4 ΩPrompt: The total is less than the smallest resistor.

You do: independent practice · 7 min

  • 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 6 questions are on the student sheet below, with answers in the key.

Exit ticket · 3 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. A 6 Ω resistor and a 12 Ω resistor are connected in parallel. What is their combined resistance, in Ω? (1/R = 1/R₁ + 1/R₂) → 4 ΩPrompt: The total is less than the smallest resistor.
  2. A 4 Ω resistor is in series with a parallel pair of 10 Ω and 15 Ω. The supply is 5 V. What current flows from the supply, in A? → 0.5 APrompt: Find the parallel pair's resistance first.

Watch out for

  • Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
  • Remembering facts without the reason: ask "why?" and "what is the evidence?"

Support and stretch

Support

  • Review first: Current and voltage rules in series and parallel circuits.
  • Use concrete materials: circuit kits (cells, wires, bulbs).
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • Explain a common mistake in writing and how to fix it.
  • Write a word problem that uses today's skill, then solve a partner's.

Homework and more practice

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

Free lesson plan from eurekami.com/lesson-plan-builder

eurekami

Total resistance of series and parallel networks

Name

Date

Score/ 6

  1. Question 1

    A 2 Ω resistor is in series with a parallel pair of 12 Ω and 6 Ω. The supply is 12 V. What current flows from the supply, in A?

    AnswerA

  2. Question 2

    Three resistors of 4 Ω, 6 Ω and 5 Ω are connected in series. What is the total resistance, in Ω?

    AnswerΩ

  3. Question 3

    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)

    AnswerΩ

  4. Question 4

    A 4 Ω resistor is in series with a parallel pair of 20 Ω and 30 Ω. The supply is 16 V. What current flows from the supply, in A?

    AnswerA

  5. Question 5

    Three resistors of 10 Ω, 30 Ω and 10 Ω are connected in series. What is the total resistance, in Ω?

    AnswerΩ

  6. Question 6

    A 12 Ω resistor and a 6 Ω resistor are connected in parallel. What is their combined resistance, in Ω? (1/R = 1/R₁ + 1/R₂)

    AnswerΩ

Free from eurekami.com

for the adult only

Answer key: Total resistance of series and parallel networks

  1. 1. 2 A

  2. 2. 15 Ω

  3. 3. 3 Ω

  4. 4. 1 A

  5. 5. 50 Ω

  6. 6. 4 Ω