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Science lesson plan · 9th grade (Year 10 in England) · 30 minutes

Efficiency

Energy

CCSS NGSS.HS-PS3-3England: KS4 Combined Science: Energy

Objective and success criteria

Students will: Efficiency.

  • 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: Conservation of energy and wasted energy

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 · 4 min

  • Quick retrieval from earlier learning (Conservation of energy and wasted energy). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. A motor is supplied with 100 J of energy. It transfers 20 J usefully. How much energy is wasted, in J? → 80 JPrompt: Energy is conserved: input = useful output + wasted output.
  2. How can wasted energy in a machine with moving parts be reduced? (make it move faster / paint it a darker colour / remove the oil / lubricate the parts to reduce friction) → lubricate the parts to reduce frictionPrompt: What causes heating where parts rub?
  3. Conservation of energy: which statement is NOT true? (Wasted energy is destroyed. / No real machine is 100% efficient. / A Sankey diagram shows useful and wasted energy. / The total energy in a closed system stays the same.) → Wasted energy is destroyed.Prompt: Can energy ever be created or destroyed?

Hook · 3 min

  • Wind up a toy or stretch an elastic band and ask where the energy goes.
  • Share the objective: Efficiency. 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 device is supplied with 200 J and transfers 30 J usefully. What is its efficiency, as a percentage?
  • Step 1: 30 ÷ 200 × 100 = 15
  • Step 2: So the answer is: 15%
  • Answer: 15 %
  • 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 device is supplied with 800 J and transfers 200 J usefully. What is its efficiency, as a percentage? → 25 %Prompt: efficiency = useful output ÷ total input
  2. A motor is 20% efficient. It is supplied with 1000 J. How much useful energy does it transfer, in J? → 200 JPrompt: useful output = efficiency × total input

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. An electric motor is 80% efficient. What happens to the other 20%? (It is turned into extra motion / It is destroyed / It is mostly wasted heating the motor and its surroundings / It is stored in the plug) → It is mostly wasted heating the motor and its surroundingsPrompt: Energy is conserved.
  2. A motor is 20% efficient. It is supplied with 1000 J. How much useful energy does it transfer, in J? → 200 JPrompt: useful output = efficiency × total input

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: Conservation of energy and wasted energy.
  • 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-9.

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

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Efficiency

Name

Date

Score/ 6

  1. Question 1

    Can a device be more than 100% efficient?

    • A. Yes, if it is new
    • B. Yes, if it is very small
    • C. Yes, if it uses a battery
    • D. No, because energy cannot be created

  2. Question 2

    A device is supplied with 800 J and transfers 120 J usefully. What is its efficiency, as a percentage?

    Answer%

  3. Question 3

    A motor is 90% efficient. It is supplied with 2000 J. How much useful energy does it transfer, in J?

    AnswerJ

  4. Question 4

    Why do LED bulbs save money compared with old filament bulbs?

    • A. They are made of glass
    • B. They use no electricity
    • C. They are brighter because they are hotter
    • D. They are more efficient, so less energy is wasted as heat

  5. Question 5

    A device is supplied with 800 J and transfers 320 J usefully. What is its efficiency, as a percentage?

    Answer%

  6. Question 6

    A motor is 30% efficient. It is supplied with 2000 J. How much useful energy does it transfer, in J?

    AnswerJ

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Answer key: Efficiency

  1. 1. D. No, because energy cannot be created

  2. 2. 15 %

  3. 3. 1800 J

  4. 4. D. They are more efficient, so less energy is wasted as heat

  5. 5. 40 %

  6. 6. 600 J