Physics 9 Chapter 6 - Work and Energy - 26

Physics 9 Chapter 6 - Work and Energy - 26

1. What is the formula of efficiency %?

a) Efficiency %= Total input energy / Required form of output
b) Efficiency %= Required form of output x Total input energy
c) Efficiency %= (Required output energy / Total input energy) x 100
d) Efficiency %= Total input energy + Required form of output

2. What is the efficiency % of an electric lamp if its input energy is 100 J and useful work done is 5 J?

a) 95%
b) 5%
c) 105%
d) 195%

3. What is the efficiency % of a petrol engine if its input energy is 100 J and useful work done is 25 J?

a) 125%
b) 25%
c) 75%
d) 175%

4. What is the efficiency % of an electric motor if its input energy is 100 J and useful work done is 80 J?

a) 120%
b) 80%
c) 20%
d) 180%

5. What is the SI unit of efficiency?

a) Watt
b) No unit
c) Pascal
d) Newton

6. What is the efficiency % of an electric fan if its input energy is 100 J and useful work done is 55 J?

a) 55%
b) 45%
c) 155%
d) 145%

7. What is the efficiency % of a solar cell if its input energy is 100 J and useful work done is 3 J?

a) 103%
b) 3%
c) 197%
d) 97%

8. What is the quantity called that tells us the rate of doing work?

a) Energy
b) Efficiency
c) Pressure
d) Power

9. What is the rate of doing work called?

a) Energy
b) Momentum
c) Torque
d) Power

10. A cyclist does 12 joules of useful work while pedalling his bike from every 100 joules of food energy which he takes. What is his efficiency?

a) 1.2%
b) 88%
c) 12%
d) 0.12%

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