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

Current, voltage and resistance (V = IR)

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: Current, voltage and resistance (V = IR).

  • 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: Circuit symbols, cells and voltage

Leads to: Series and parallel circuits; Electrical power, charge and energy; Charge, current and time (Q = I t)

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 (Circuit symbols, cells and voltage). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. A circle with the letter M inside stands for… (a motor / a mirror / a meter / a magnet) → a motorPrompt: The letter is a clue.
  2. A gap in a line with a small hinged line (lifted up) stands for… (an open switch / a closed switch / a cell / a bulb) → an open switchPrompt: The gap means the circuit is broken.
  3. Why do scientists draw circuits with symbols instead of pictures? (Symbols make circuits work better / Symbols are quick to draw and understood everywhere / Pictures are not allowed / Symbols are prettier) → Symbols are quick to draw and understood everywherePrompt: Think about sharing a plan with someone in another country.

Hook · 3 min

  • Show a circuit with a gap and ask why the bulb doesn't light.
  • Share the objective: Current, voltage and resistance (V = IR). 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: A current of 2 A flows through a 12 Ω resistor. What is the potential difference (voltage) across it, in V?
  • Step 1: V = 2 × 12 = 24
  • Step 2: So the answer is: 24 V
  • Answer: 24 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. A current of 4 A flows through a 5 Ω resistor. What is the potential difference (voltage) across it, in V? → 20 VPrompt: V = I × R
  2. A 12 V supply is connected across a 6 Ω resistor. What current flows, in A? → 2 APrompt: Rearrange V = I R to find I.

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 1 V supply is connected across a 2 Ω resistor. What current flows, in A? → 0.5 APrompt: Rearrange V = I R to find I.
  2. A 2.5 V battery drives a current of 0.5 A through a lamp. What is the resistance of the lamp, in Ω? → 5 ΩPrompt: R = V ÷ I

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: Circuit symbols, cells and voltage.
  • 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: Series and parallel circuits; Electrical power, charge and energy; Charge, current and time (Q = I t).
  • 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

Current, voltage and resistance (V = IR)

Name

Date

Score/ 6

  1. Question 1

    A 60 V supply is connected across a 20 Ω resistor. What current flows, in A?

    AnswerA

  2. Question 2

    A 1.5 V battery drives a current of 0.25 A through a lamp. What is the resistance of the lamp, in Ω?

    AnswerΩ

  3. Question 3

    A current of 0.5 A flows through a 12 Ω resistor. What is the potential difference (voltage) across it, in V?

    AnswerV

  4. Question 4

    A 3 V supply is connected across a 2 Ω resistor. What current flows, in A?

    AnswerA

  5. Question 5

    A 24 V battery drives a current of 2 A through a lamp. What is the resistance of the lamp, in Ω?

    AnswerΩ

  6. Question 6

    A current of 2 A flows through a 5 Ω resistor. What is the potential difference (voltage) across it, in V?

    AnswerV

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Answer key: Current, voltage and resistance (V = IR)

  1. 1. 3 A

  2. 2. 6 Ω

  3. 3. 6 V

  4. 4. 1.5 A

  5. 5. 12 Ω

  6. 6. 10 V