1. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 3.1 – Questions and answers 1What energy transfers are the following devices designed to bring about? (a) electric drill AElectric to kinetic (b) fan heater AElectric to kinetic and heat (c) television. A Electric to light and sound.

2. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 3.1 – Questions and answers 2How is energy wasted in the devices in question 1? A(a) Heat and sound. (b) Sound. (c) Heat.

3. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 3.1 – Questions and answers 3Name two electrical devices (other than those in question 1) that are designed to transfer electrical energy into: (a) heating AAny two from: cooker, toaster, microwave, electric fire, hair dryer, iron, etc. (b) light AAny two from: light bulb, LED, computer, etc.

4. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 3.1 – Questions and answers 3(c) sound AAny two from: radio, computer, stereo system, MP3 player, etc. (d) movement. AAny two from: food mixer, hair dryer, lawnmower, electric saw (or other DIY tools), etc.; do not accept television (some students think the ‘moving’ picture means that kinetic energy is involved) unless electrons in CRT are specified.

5. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 3.1 – Questions and answers 4A 50 W radio is switched on for 3 hours. How much energy does it use? AEnergy = power × time = 50 W × (3 × 3600) s = 540 000 J (or 540 kJ).

6. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 3.1 – Questions and answers 5 A tumble dryer uses 2700 kJ of electrical energy when it is used for half an hour. What power is the tumble dryer? A Power = energy/time = 2 700 000 J/(30 × 60) s = 1500 W (or 1.5 kW).

7. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 3.1 – Questions and answers 6A computer uses 2400 kJ of energy. Its power is 65 W. How long was it switched on for? Give your answer in hours, minutes and seconds to the nearest second. ATime = energy/power = 2 400 000 J/65 W = 36 923 seconds. This is 10.256 hours = 10 hours 15.38 minutes = 10 h 15 m 23 s.

8. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 3.1 – Questions and answers 7An electric oven has a power of 3 kW. A cake takes 40 minutes to bake. (a) What is the maximum amount of energy the oven will use to bake the cake? AEnergy = power × time = 3000 W × (40 × 60) s = 7 200 000 J (or 7200 kJ).

9. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 3.1 – Questions and answers 7(b) Explain why this is a maximum amount. (Hint: think about what the thermostat in an oven does.) AThe oven takes some time to warm up, so some energy will have been used before the cake is put in. Once the oven has reached the correct temperature the heating element is switched off until the temperature drops a little, so the oven is not using electricity for all the time it is switched on.

10. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 3.1 – Questions and answers 8 ‘The increasing ownership of toasters could help to reduce the amount of electricity used.’ Explain this statement. (Hint: think about how you would make toast if you did not have a toaster.)

11. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 3.1 – Questions and answers A A toaster has the heating elements very close to the bread, so not much energy is wasted. A grill is usually further away from the bread, and has a much larger heating element and so is likely to have a higher power. Unless a lot of toast is being made some of the element will just be heating air and so wasting energy. So, although some electricity will have been used when the toaster was made, taking into account the savings in electricity use when a toaster is used instead of a grill, owning a toaster might save on electricity use overall.