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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. Why do scientists draw circuits with symbols instead of pictures? (Symbols are quick to draw and understood everywhere / Symbols are prettier / Symbols make circuits work better / Pictures are not allowed) → Symbols are quick to draw and understood everywherePrompt: Think about sharing a plan with someone in another country.
  2. A circle with a cross inside it stands for… (a resistor / a cell / a lamp (bulb) / a buzzer) → a lamp (bulb)Prompt: It looks like a glowing filament.
  3. A gap in a line with a small hinged line (lifted up) stands for… (an open switch / a cell / a bulb / a closed switch) → an open switchPrompt: The gap means the circuit is broken.

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 0.5 A flows through a 6 Ω resistor. What is the potential difference (voltage) across it, in V? → 3 VPrompt: V = I × R
  2. A 6 V supply is connected across a 4 Ω resistor. What current flows, in A? → 1.5 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 current of 1.5 A flows through a 10 Ω resistor. What is the potential difference (voltage) across it, in V? → 15 VPrompt: V = I × R
  2. A 3 V supply is connected across a 2 Ω resistor. What current flows, in A? → 1.5 APrompt: Rearrange V = I R to find 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 30 V battery drives a current of 2 A through a lamp. What is the resistance of the lamp, in Ω?

    AnswerΩ

  2. Question 2

    A current of 3 A flows through a 2 Ω resistor. What is the potential difference (voltage) across it, in V?

    AnswerV

  3. Question 3

    A 15 V supply is connected across a 5 Ω resistor. What current flows, in A?

    AnswerA

  4. Question 4

    A current of 1 A flows through a 20 Ω resistor. What is the potential difference (voltage) across it, in V?

    AnswerV

  5. Question 5

    A 24 V supply is connected across a 8 Ω resistor. What current flows, in A?

    AnswerA

  6. Question 6

    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

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

  1. 1. 15 Ω

  2. 2. 6 V

  3. 3. 3 A

  4. 4. 20 V

  5. 5. 3 A

  6. 6. 6 Ω