Conservation of energy and efficiency Quiz
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5 questions, one answer each
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1. A kettle takes in 2000 J and transfers 1800 J to the water. What is its efficiency?
- A. 10%
- B. 90%
- C. 111%
- D. 9%
2. Where does most of the wasted energy end up?
- A. In the chemical store of the device
- B. It is destroyed
- C. In the thermal store of the surroundings
- D. In the elastic store
3. Which action improves the efficiency of a bicycle?
- A. Adding oil to the chain
- B. Making the tyres rougher
- C. Adding mud to the wheels
- D. Letting the chain rust
4. A device has an efficiency of 25% and a total input of 800 J. How much useful energy does it give out?
- A. 25 J
- B. 32 J
- C. 600 J
- D. 200 J
5. A student claims a machine is 120% efficient. What is wrong with this claim?
- A. Nothing, because new machines can be above 100% efficient
- B. Efficiency must always be exactly 100%
- C. Efficiency can only be measured in joules
- D. It would mean more energy came out than went in, which is impossible