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

Current and voltage rules in series and parallel circuits

Electricity and magnetism

CCSS NGSS.MS-PS2-3CCSS NGSS.HS-PS3-5England: KS3 Physics: Electricity and electromagnetismEngland: GCSE Combined Science: Electricity (series and parallel)

Objective and success criteria

Students will: Current and voltage rules in 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: Series and parallel circuits

Leads to: Total resistance of series and parallel networks

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 (Series and parallel circuits). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. A parallel circuit has two branches. The current in one branch is 1 A and in the other is 0.5 A. What is the current from the battery, in A? → 1.5 APrompt: In parallel, the branch currents add up to the total current.
  2. Why are lights in a house wired in parallel? (If one breaks, they all go off / It uses less wire / So the current is the same everywhere / Each can be switched on and off separately and gets the full voltage) → Each can be switched on and off separately and gets the full voltagePrompt: What happens in series if one bulb breaks?
  3. Series and parallel: which statement is NOT true? (In a series circuit, if one bulb breaks, the others go out. / In series, total resistance is the sum of the resistances. / In a parallel circuit, the voltage across each branch is the same. / Adding resistors in parallel increases the total resistance.) → Adding resistors in parallel increases the total resistance.Prompt: Is current used up in a circuit?

Hook · 3 min

  • Show a circuit with a gap and ask why the bulb doesn't light.
  • Share the objective: Current and voltage rules in 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 lamps are connected in series to a 12 V battery. The voltage across the first lamp is 8 V. What is the voltage across the second lamp, in V?
  • Step 1: 12 − 8 = 4
  • Step 2: So the answer is: 4 V
  • Answer: 4 V
  • 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 lamps are connected in series to a 4.5 V battery. The voltage across the first lamp is 3 V. What is the voltage across the second lamp, in V? → 1.5 VPrompt: In series, the supply voltage is shared between components.
  2. Two lamps are in parallel. The current through one branch is 0.8 A and through the other is 1.2 A. What current flows from the battery, in A? → 2 APrompt: In parallel, the current splits between branches.

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 2.8 A current leaves a battery and splits into two parallel branches. One branch carries 0.8 A. What current flows in the other branch, in A? → 2 APrompt: Current is not used up; it is shared between branches.
  2. In a parallel circuit with three lamps, one lamp breaks. What happens to the other two? (they all go out / they stay lit / they get dimmer / they flicker and stop) → they stay litPrompt: A parallel circuit has more than one loop.

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: 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

  • Move on to: Total resistance of series and parallel networks.
  • 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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Current and voltage rules in series and parallel circuits

Name

Date

Score/ 6

  1. Question 1

    Two lamps are in parallel. The current through one branch is 1.5 A and through the other is 2 A. What current flows from the battery, in A?

    AnswerA

  2. Question 2

    In a series circuit with three lamps, one lamp breaks. What happens to the other two?

    • A. they stay the same
    • B. they go out
    • C. only one goes out
    • D. they get brighter

  3. Question 3

    Two lamps are connected in series to a 6 V battery. The voltage across the first lamp is 1.5 V. What is the voltage across the second lamp, in V?

    AnswerV

  4. Question 4

    A 2 A current leaves a battery and splits into two parallel branches. One branch carries 0.8 A. What current flows in the other branch, in A?

    AnswerA

  5. Question 5

    Two identical lamps are connected in parallel to a 6 V battery. What is the voltage across each lamp?

    • A. 0 V
    • B. 12 V
    • C. 6 V
    • D. 3 V

  6. Question 6

    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?

    AnswerV

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Answer key: Current and voltage rules in series and parallel circuits

  1. 1. 3.5 A

  2. 2. B. they go out

  3. 3. 4.5 V

  4. 4. 1.2 A

  5. 5. C. 6 V

  6. 6. 3 V