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Science lesson plan · 8th grade (Year 9 in England) · 30 minutes

Series and parallel circuits

Electricity and magnetism

CCSS NGSS.HS-PS3-1England: KS3 Physics: Electricity and electromagnetism (current electricity)England: KS4 Combined Science: Electricity

Objective and success criteria

Students will: Series and parallel circuits.

  • 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, voltage and resistance (V = IR)

Leads to: Current and voltage rules in series and parallel circuits

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, voltage and resistance (V = IR)). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. A current of 3 A flows through a 20 Ω resistor. What is the potential difference (voltage) across it, in V? → 60 VPrompt: V = I × R
  2. A 12 V supply is connected across a 8 Ω resistor. What current flows, in A? → 1.5 APrompt: Rearrange V = I R to find I.
  3. A 3 V battery drives a current of 0.25 A through a lamp. What is the resistance of the lamp, in Ω? → 12 ΩPrompt: R = V ÷ I

Hook · 3 min

  • Show a circuit with a gap and ask why the bulb doesn't light.
  • Share the objective: Series and parallel circuits. 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: Two resistors of 8 Ω and 14 Ω are connected in series. What is their total resistance, in Ω?
  • Step 1: 8 + 14 = 22
  • Step 2: So the answer is: 22 Ω
  • Answer: 22 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. Two resistors of 5 Ω and 20 Ω are connected in series. What is their total resistance, in Ω? → 25 ΩPrompt: In series, resistances add.
  2. How is an ammeter connected to measure the current through a lamp? (in series with the lamp / in parallel with the lamp / across the battery only / it is not connected) → in series with the lampPrompt: The current must pass through the meter.

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. Two resistors of 12 Ω and 19 Ω are connected in series. What is their total resistance, in Ω? → 31 ΩPrompt: In series, resistances add.
  2. Series and parallel: which statement is NOT true? (Voltmeters are connected in parallel. / Ammeters are connected in parallel. / In series, total resistance is the sum of the resistances. / In a series circuit, if one bulb breaks, the others go out.) → Ammeters are connected in parallel.Prompt: Is current used up in a circuit?

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, voltage and resistance (V = IR).
  • 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

  • Move on to: Current and voltage rules in series and parallel circuits.
  • 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-8.

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

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Series and parallel circuits

Name

Date

Score/ 6

  1. Question 1

    Series and parallel: which statement is NOT true?

    • A. In a series circuit, current is used up by each bulb.
    • B. In a parallel circuit, the voltage across each branch is the same.
    • C. In series, total resistance is the sum of the resistances.
    • D. Voltmeters are connected in parallel.

  2. Question 2

    Two lamps are in series with a 12 V battery. The voltage across one lamp is 11 V. What is the voltage across the other lamp, in V?

    AnswerV

  3. Question 3

    Adding more bulbs in parallel to a battery (each in its own branch) makes each bulb…

    • A. explode
    • B. go out
    • C. stay about as bright as before
    • D. get much dimmer

  4. Question 4

    Two resistors of 4 Ω and 18 Ω are connected in series. What is their total resistance, in Ω?

    AnswerΩ

  5. Question 5

    Two lamps are in series with a 24 V battery. The voltage across one lamp is 7 V. What is the voltage across the other lamp, in V?

    AnswerV

  6. Question 6

    Why are lights in a house wired in parallel?

    • A. It uses less wire
    • B. So the current is the same everywhere
    • C. Each can be switched on and off separately and gets the full voltage
    • D. If one breaks, they all go off

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Answer key: Series and parallel circuits

  1. 1. A. In a series circuit, current is used up by each bulb.

  2. 2. 1 V

  3. 3. C. stay about as bright as before

  4. 4. 22 Ω

  5. 5. 17 V

  6. 6. C. Each can be switched on and off separately and gets the full voltage