Electrical energy

Summary questionsa) Electrical energy is energy transfer by an electric ______________.

b) Uses of electrical devices include:

heating (e.g. heaters).

lighting (e.g. ____________________________).

making objects move (e.g. ____________________________).

creating sound (e.g. ____________________________).

creating visual images (e.g. ___________________________).

a) The unit of power is the ______________.

b) 1 kilowatt = ______________ watts.

c) Power (in watts) =

a) One kilowatt hour (kW h) is the ____________ supplied to a 1 kilowatt device in one hour.

b) Energy transferred (in kW h) = ______________ of device (in kW) time in use (in __________).

c) Cost of electricity = number of kW h cost per ______________.

a) The National Grid is a network of cables and ____________________________.

b) i) A ______________ transformer steps the voltage _________ from a power station up to the grid voltage.

ii) A ______________ transformer steps the grid voltage ___________ to the voltage used in our homes and offices.

c) The higher the grid voltage is, the ____________ efficient the grid is.

1A The average power of one washing machine is 2400 watts.

2400 watts is equal to . . .

1 0.24kW2 2.40kW3 24kW4 240kW

1B

How much energy, in kilowatt-hours, is transferred when a 2400 watt washing machine is used for 60 minutes?

1 2.42 403 1444 144 000

1C The A-rated washing machine is used for 300 standard washing cycles per year.

How much energy does this number of cycles transfer?

1 270kWh2 1500kWh3 2700kWh4 3600kWh

1D

A large family uses the A-rated washing machine for 500 standard washing cycles in a year.

1 kilowatt-hour of electricity costs 12p.

How much does the washing machine cost to run each year?

1 £402 £41.603 £544 £60

QUESTION TWO

A village is many kilometres away from a supply of mains electricity. The sun shines for at least a few hours nearly every day. The villagers want a supply of electricity for a radio receiver.

The table shows the costs of two different ways of providing the electricity over a 20-year period.

2A What are the total costs over the 20-year period of the different ways of providing electricity?

2B One disadvantage of using solar cells and rechargeable batteries is that . . .

1 new batteries are needed more often.2 the radio could not be used at night.3 they are more expensive in the long run.4 they cost more in the first place.

2C Another battery of solar cells has a maximum output of 1 kW. The battery, when used in the UK, produces, on average, 10 % of its maximum output. The battery costs £ 4000 and has an expected life of 200 000 hours. The cells have no maintenance costs.

What is the cost of each kilowatt-hour of electricity produced by the battery of solar cells whenused in the UK?

1 20 p2 25 p3 40 p4 50 p

2D Electricity from solar cells is more expensive than electricity generated in power stations.

Which of the following would make the cost of electricity from solar cells cheaper?

1 A decrease in the cost of fuel for normal types of power station.2 Developing solar cells that are smaller.3 Developing other alternative energy technologies.4 Reducing the cost of solar cells by mass production.

QUESTION THREE

This question is about an electric iron. The power of the iron is 1.2kW.

3A The base of the iron radiates energy.

It will radiate least energy when the base is . . .

1 at a high temperature and black.2 at a high temperature and shiny.3 at a low temperature and black.4 at a low temperature and shiny.

7B What is the maximum quantity of energy, in joules, that can be transformed by the iron in one hour?

1 72 J2 4320 J3 72 000 J4 4 320 000 J

7C When the iron is used for one hour, less than the calculated maximum amount of energy is transformed.Why is this?

1 Some energy is provided by the person doing the ironing.2 Some energy is transferred to the surroundings.3 The ironing board is covered with an insulator.4 The iron switches off at times to keep it at the correct temperature.

7D Electricity costs 10 p per kilowatt-hour. In one week, the iron uses electricity for a total of 90 minutes.Calculate the cost of this electricity.

1 £ 0.152 £ 0.183 £ 0.904 £ 1.08