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Science lesson plan · 7th grade (Year 8 in England) · 60 minutes

Kilowatt-hours and the cost of electricity

Energy

CCSS NGSS.MS-PS3-5CCSS NGSS.SEP 5England: KS3 Physics: Energy (energy costs)

Objective and success criteria

Students will: Kilowatt-hours and the cost of electricity.

  • 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: Identify energy stores in everyday situations

Leads to: the next skill in this area.

Materials: Wind-up toys or a pendulum, Energy transfer diagrams, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).

Warm-up · 6 min

  • Quick retrieval from earlier learning (Identify energy stores in everyday situations). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. Which energy store is the main one here: wind turning a turbine? (kinetic store / nuclear store / gravitational potential store / chemical store) → kinetic storePrompt: Is it moving, high up, stretched, hot, a fuel or food, or atomic?
  2. An electric car's battery runs down as it drives up a hill. Which stores gain energy? (the car's nuclear store / the car's gravitational potential store and the thermal store of the surroundings / only the battery's chemical store / no store gains energy) → the car's gravitational potential store and the thermal store of the surroundingsPrompt: The car gets higher, and the motor gets warm.
  3. Energy stores: which statement is NOT true? (Energy is measured in joules (J). / Food contains energy in a chemical store. / A stationary book on a high shelf has no energy. / A faster object has more energy in its kinetic store.) → A stationary book on a high shelf has no energy.Prompt: Is light a store or a way of transferring energy?

Hook · 6 min

  • Wind up a toy or stretch an elastic band and ask where the energy goes.
  • Share the objective: Kilowatt-hours and the cost of electricity. Read the success criteria together.

I do: model it · 12 min

  • Work through the example out loud, saying why you do each step, not just what you do.
  • Example: An oven with a power of 1.5 kW is used for 6 hours. How much energy does it transfer, in kWh?
  • Step 1: 1.5 × 6 = 9
  • Step 2: So the answer is: 9 kWh
  • Answer: 9 kWh
  • Pause after each step and ask a student to say what comes next.

We do: guided practice · 12 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. An oven with a power of 3 kW is used for 6 hours. How much energy does it transfer, in kWh? → 18 kWhPrompt: energy (kWh) = power (kW) × time (h)
  2. Electricity costs 28p per kWh. How much does 10 kWh cost, in pence? → 280Prompt: cost = energy used (kWh) × price per kWh

You do: independent practice · 17 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 · 7 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. An oven with a power of 3 kW is used for 2 hours. How much energy does it transfer, in kWh? → 6 kWhPrompt: energy (kWh) = power (kW) × time (h)
  2. Electricity costs 20p per kWh. How much does 2 kWh cost, in pence? → 40Prompt: cost = energy used (kWh) × price per kWh

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: Identify energy stores in everyday situations.
  • Use concrete materials: wind-up toys or a pendulum.
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • 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-7.

Free lesson plan from eurekami.com/lesson-plan-builder

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Kilowatt-hours and the cost of electricity

Name

Date

Score/ 8

  1. Question 1

    An electric heater rated at 2000 W runs for 90 minutes. Electricity costs 24p per kWh. What does it cost, in pence?

    Answer

  2. Question 2

    A games console with a power of 2.5 kW is used for 2 hours. How much energy does it transfer, in kWh?

    AnswerkWh

  3. Question 3

    Electricity costs 28¢ per kWh. How much does 20 kWh cost, in cents?

    Answer

  4. Question 4

    An electric heater rated at 2000 W runs for 30 minutes. Electricity costs 30p per kWh. What does it cost, in pence?

    Answer

  5. Question 5

    An oven with a power of 1.5 kW is used for 6 hours. How much energy does it transfer, in kWh?

    AnswerkWh

  6. Question 6

    Electricity costs 30c per kWh. How much does 2 kWh cost, in euro cents?

    Answer

  7. Question 7

    An electric heater rated at 1500 W runs for 45 minutes. Electricity costs 24¢ per kWh. What does it cost, in cents?

    Answer

  8. Question 8

    A heater with a power of 1.5 kW is used for 0.5 hours. How much energy does it transfer, in kWh?

    AnswerkWh

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Answer key: Kilowatt-hours and the cost of electricity

  1. 1. 72

  2. 2. 5 kWh

  3. 3. 560

  4. 4. 30

  5. 5. 9 kWh

  6. 6. 60

  7. 7. 27

  8. 8. 0.75 kWh