Science 9 · Unit 3: Forces and energy · Cambridge Lower Secondary Science Stage 9

Questions

1. 1. Every time 100 J of electrical energy is supplied to a lamp, 10 J is changed to light energy. How much is changed to thermal energy?

   • 10 J
   • 90 J
   • 100 J
   • 110 J
   Check

2. 2. Every time 100 J of electrical energy is supplied to a lamp, 10 J is changed to light energy and 90 J to thermal energy. Which energy is useful and which is wasted?

   • Both are wasted.
   • Thermal energy is useful; light is wasted.
   • Light is useful; thermal energy is wasted.
   • Electrical energy is wasted.
   Check

3. 3. What happens to the wasted energy from a machine?

   • It spreads out into the surroundings, mostly as thermal energy.
   • It turns back into fuel.
   • It is destroyed.
   • It goes back into the power supply.
   Check

4. 4. Sofia's LED flashlight uses 18 J of electrical energy. 7 J is wasted as thermal energy. Anna says that 12 J is changed to light. Is Anna right?

   • Yes, because 12 J + 7 J = 18 J.
   • Yes, because the flashlight makes 1 J of extra energy.
   • No. All 18 J is changed to light.
   • No. Only 18 − 7 = 11 J can be changed to light.
   Check

5. 5. When energy is conserved, what happens to the total quantity of energy?

   • It increases.
   • New energy is made.
   • Some of it is destroyed.
   • It stays the same.
   Check

6. 6. Which statement shows conservation of energy in an electric lamp?

   • The energy input to the lamp equals the energy output from the lamp.
   • The lamp should be switched off when not in use.
   • The energy output is greater than the energy input.
   • The energy input is greater than the energy output.
   Check

7. 7. 100 J of electrical energy is supplied to a motor. It is changed to thermal and kinetic energy. What is the total quantity of thermal and kinetic energy changed in the motor?

   • less than 100 J, because some is used up
   • 50 J
   • 200 J
   • 100 J
   Check

8. 8. A car engine changes chemical energy to thermal and kinetic energy. A total of 3500 J of thermal and kinetic energy are changed. What quantity of chemical energy is changed in the engine?

   • 1750 J
   • 7000 J
   • more than 3500 J
   • 3500 J
   Check

9. 9. What is the law of conservation of energy?

   • Energy can be made in power stations.
   • Energy is used up when we use it.
   • Energy should be saved by switching things off.
   • Energy cannot be made or destroyed, only changed from one form to another.
   Check

10. 10. An electric lamp changes electrical energy into light and thermal energy. How does the law of conservation of energy apply?

    • The light energy plus the thermal energy equals the electrical energy supplied.
    • The light energy equals the electrical energy, and the heat is extra.
    • The lamp makes more light energy than the electrical energy it takes in.
    • Some electrical energy is destroyed inside the lamp.
    Check

11. 11. Sofia takes in more chemical energy from food on days when she is playing sports than on days when she is resting. Why?

    • She changes more energy to kinetic and thermal energy, and that energy has to come from her food.
    • Exercise destroys energy, so she needs more.
    • Food has more energy on sports days.
    • Sport makes new energy in her muscles.
    Check

12. 12. An electric motor changes 65% of its electrical energy into kinetic energy and the rest into thermal energy. What percentage is changed to thermal energy?

    • 6.5%
    • 165%
    • 35%
    • 65%
    Check

13. 13. An electric lamp takes in 1000 J of electrical energy. The lamp wastes 850 J of energy. What quantity of useful energy does it change?

    • 850 J
    • 1000 J
    • 150 J
    • 1850 J
    Check

14. 14. A motorcycle engine uses 2400 J of chemical energy in fuel. 1000 J is changed to thermal energy and 600 J to sound energy. The rest is changed to kinetic energy. How much kinetic energy is changed?

    • 800 J
    • 1800 J
    • 4000 J
    • 1400 J
    Check

15. 15. A television changes electrical energy into thermal, light and sound energy. 50% is changed to thermal and 30% to light. What percentage is changed to sound?

    • 20%
    • 10%
    • 80%
    • 30%
    Check

16. 16. In an energy flow diagram for a television, which arrow should be the widest?

    • the thermal energy going out
    • the light energy going out
    • the sound energy going out
    • the electrical energy going in
    Check