Electric kettle

You are part of a design team. Your task is to create a kettle that is affordable, sensible with energy and does not end up as electronic waste after its first fault. The budget is limited – every decision costs something and brings something.

• Students calculate the heat needed to heat water using Q = m · c · ΔT and convert joules to watt-hours.
• Students explain the difference between ideal and actual energy consumption (efficiency, heat losses).
• Students understand that extending lifetime and repairability can matter more for a product's impact than recycling alone.
• Students can argue for a trade-off between purchase price, running costs and lifetime.

1. 1

   Body materialDecision

   What will the kettle body be made of?

2. 2

   Heating element and efficiencyDecision

   How good will the heating element and thermal insulation be?

3. 3

   Amount of water heatedDecision

   How much water will you usually heat in the kettle?

4. 4

   Physics mini-task

   How much energy is needed to heat water in a kettle? Calculate the ideal case without losses, then compare it with how much energy the kettle actually draws from the socket.

5. 5

   RepairabilityDecision

   How repairable will the kettle be?

6. 6

   Lifetime and warrantyDecision

   What components and warranty will the kettle get?

7. 7

   End of lifeDecision

   What happens to the kettle at the end of its life?

Linear model

Extract – make – use – throw away. The material leaves the economy after use.

Circular economy

Products and materials are kept in circulation as long as possible: by repair, reuse and recycling.

Efficiency (η)

The share of usefully used energy in the energy supplied. The rest are losses, most often heat.

Specific heat capacity

The heat needed to warm 1 kg of a substance by 1 °C. For water it is 4 180 J/(kg·°C).

Modular design

A product made of replaceable parts, so that only what failed can be repaired.

Take-back

The manufacturer takes the product back at the end of its life and arranges reuse or recycling.

• Q = m · c · ΔTThe heat needed to warm water of mass m and specific heat capacity c by a temperature change ΔT.
• 1 Wh = 3 600 JConversion between the SI unit of energy and the unit used on electricity meters.
• E = Q ÷ ηActual energy drawn at efficiency η. For 1 l of water and η = 0.85 this gives ≈ 109 Wh.

1. 5 min

   Introduction

   A short discussion: what happens to a broken kettle? The difference between the linear and circular model.

2. 20 min

   Work in the app

   Pairs go through seven steps including the physics mini-task. Encourage them to agree on each decision.

3. 10 min

   Discussion

   Compare the pairs' results and use the discussion questions from the results screen.

Total 35 minutes. See the teacher guide for shorter and longer variants.

• How much water you heat can matter more than how efficient the kettle is: heating 1.7 l instead of 0.5 l wastes more energy than the gap between an 80% and a 92% efficient heating element.
• Repairability and a long lifetime reduce the need to manufacture new appliances – a benefit that the energy calculation alone does not show.
• Recycling is the last resort: manufacturer take-back (reuse of working parts) beats plain e-waste collection, which beats mixed waste.

• “Recycled plastic makes the kettle sustainable.”

  In reality: Material is only one stage. Without repairability and a long lifetime the kettle still ends up as waste early.

• “Higher efficiency always pays off.”

  In reality: Efficiency saves energy per heating but raises the purchase price; the saving depends on how much water is heated and how often.

• “Joules and watt-hours are different kinds of quantity.”

  In reality: Both measure energy: 1 Wh = 3 600 J. Watt-hours are simply the unit used on electricity meters.

1. 1.Why can heating only the necessary amount of water be more effective than buying a more expensive kettle with higher efficiency?
2. 2.Which decision raised the price but reduced the need to manufacture a new appliance?
3. 3.Who should bear responsibility for an appliance's end of life – the manufacturer, the retailer or the consumer?

• Homework: find the power (W) on a kettle at home, time one boil and estimate its energy with E = P · t.
• Compare a week of heating 0.5 l with a week of heating 1.7 l for a household – how many Wh are wasted?
• Debate: should manufacturers be legally responsible for taking appliances back at the end of life?