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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 0.5 A flows through a 20 Ω resistor. What is the potential difference (voltage) across it, in V? → 10 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 7.5 V battery drives a current of 0.5 A through a lamp. What is the resistance of the lamp, in Ω? → 15 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 3 Ω and 14 Ω are connected in series. What is their total resistance, in Ω? → 17 ΩPrompt: In series, resistances add.
  2. Why are lights in a house wired in parallel? (So the current is the same everywhere / Each can be switched on and off separately and gets the full voltage / It uses less wire / If one breaks, they all go off) → 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. 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? → 17 VPrompt: In series, the battery voltage is shared between the components.
  2. Series and parallel: which statement is NOT true? (Voltmeters 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.) → 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

eurekami

Series and parallel circuits

Name

Date

Score/ 8

  1. Question 1

    Why are lights in a house wired in parallel?

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

  2. Question 2

    Series and parallel: which statement is NOT true?

    • A. Voltmeters are connected in parallel.
    • B. Adding resistors in parallel increases the total resistance.
    • C. In a parallel circuit, the voltage across each branch is the same.
    • D. In series, total resistance is the sum of the resistances.

  3. Question 3

    A parallel circuit has two branches. The current in one branch is 0.3 A and in the other is 2 A. What is the current from the battery, in A?

    AnswerA

  4. Question 4

    Two lamps are in series with a 24 V battery. The voltage across one lamp is 5 V. What is the voltage across the other lamp, in V?

    AnswerV

  5. Question 5

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

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

  6. Question 6

    A parallel circuit has two branches. The current in one branch is 1.5 A and in the other is 2 A. What is the current from the battery, in A?

    AnswerA

  7. Question 7

    In a series circuit, the current is…

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

  8. Question 8

    Two resistors of 2 Ω and 11 Ω are connected in series. What is their total resistance, in Ω?

    AnswerΩ

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Answer key: Series and parallel circuits

  1. 1. B. Each can be switched on and off separately and gets the full voltage

  2. 2. B. Adding resistors in parallel increases the total resistance.

  3. 3. 2.3 A

  4. 4. 19 V

  5. 5. B. stay about as bright as before

  6. 6. 3.5 A

  7. 7. C. the same at every point

  8. 8. 13 Ω