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Science lesson plan · 8th grade (Year 9 in England) · 45 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 · 5 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 1.5 A flows through a 20 Ω resistor. What is the potential difference (voltage) across it, in V? → 30 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 48 V battery drives a current of 2 A through a lamp. What is the resistance of the lamp, in Ω? → 24 ΩPrompt: R = V ÷ I

Hook · 5 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 · 10 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 · 10 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 2 Ω and 5 Ω are connected in series. What is their total resistance, in Ω? → 7 ΩPrompt: In series, resistances add.
  2. Why are lights in a house wired in parallel? (It uses less wire / If one breaks, they all go off / Each can be switched on and off separately and gets the full voltage / So the current is the same everywhere) → Each can be switched on and off separately and gets the full voltagePrompt: What happens in series if one bulb breaks?

You do: independent practice · 10 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 8 questions are on the student sheet below, with answers in the key.

Exit ticket · 5 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. Series and parallel: which statement is NOT true? (Adding resistors in parallel increases the total resistance. / In a series circuit, if one bulb breaks, the others go out. / In a parallel circuit, the voltage across each branch is the same. / In series, total resistance is the sum of the resistances.) → Adding resistors in parallel increases the total resistance.Prompt: Is current used up in a circuit?
  2. Two resistors of 10 Ω and 10 Ω are connected in series. What is their total resistance, in Ω? → 20 ΩPrompt: In series, resistances add.

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

eurekami

Series and parallel circuits

Name

Date

Score/ 8

  1. Question 1

    Series and parallel: which statement is NOT true?

    • A. Voltmeters are connected in parallel.
    • B. In a parallel circuit, the voltage across each branch is the same.
    • C. In a series circuit, if one bulb breaks, the others go out.
    • D. Ammeters are connected in parallel.

  2. Question 2

    How is an ammeter connected to measure the current through a lamp?

    • A. in series with the lamp
    • B. it is not connected
    • C. in parallel with the lamp
    • D. across the battery only

  3. Question 3

    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

  4. Question 4

    A parallel circuit has two branches. The current in one branch is 1 A and in the other is 0.4 A. What is the current from the battery, in A?

    AnswerA

  5. Question 5

    Why are lights in a house wired in parallel?

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

  6. Question 6

    Two resistors of 14 Ω and 20 Ω are connected in series. What is their total resistance, in Ω?

    AnswerΩ

  7. Question 7

    In a series circuit, the current is…

    • A. used up by each component
    • B. zero at the battery
    • C. biggest after the bulb
    • D. the same at every point

  8. Question 8

    Two lamps are in series with a 6 V battery. The voltage across one lamp is 3 V. What is the voltage across the other lamp, in V?

    AnswerV

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Answer key: Series and parallel circuits

  1. 1. D. Ammeters are connected in parallel.

  2. 2. A. in series with the lamp

  3. 3. 17 V

  4. 4. 1.4 A

  5. 5. A. Each can be switched on and off separately and gets the full voltage

  6. 6. 34 Ω

  7. 7. D. the same at every point

  8. 8. 3 V