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| Question | Answer |
| What do electrical appliances usually display a power rating in? | Electrical appliances usually display a power rating in watts (W) or kilowatts (kW). |
| What is the word equation for power by voltage? | power = voltage x current |
| PRACTICE QUESTION What is the power rating of a kettle working at 9 amps (A) on the mains supply of 230 volts (V)? | power = voltage x current power = 9 x 230 power = 2070 W |
| What is the word equation for energy supplied by power? | energy supplied = power x time |
| What is the unit of electrical energy used in the home? | The unit for electrical energy used in the home is the kilowatt-hour (kWh). |
| What is the word equation for cost of electricity used by energy used? | cost of electricity used = energy used x cost per kWh |
| PRACTICE QUESTION Calculate the cost of using a 250 W television for 30 minutes if one kWh of electricity costs 10p? | energy used = power x time energy used = 0.25 x 0.5 energy used = 0.125 kWh cost of electricity = energy used x cost per kWh cost of electricity = 0.125 x 10 cost of electricity = 1.25p |
| Why do we pay less for electricity during the night? | We pay less for electricity during the night when not as much is needed, but it still has to be produced. |
| Some energy sources are more appropriate than others in a particular situation. The choice of energy sources depends on which several factors? | The choice of energy sources depends on several factors: - availability - ease of extraction - effect on the environment - associated risks. |
| What is the National Grid? | The National Grid is a series of transformers and power lines that transport electricity from the power station to the consumer. |
| In the National Grid what are transformers used for? | In the National Grid, transformers are used to step up the voltage to as high as 400 000 V. |
| What does the high voltage lead to? | The high voltage leads to: - reduced energy loss - reduced distribution costs - cheaper electricity for consumers. |
| What are transformers then used again for? | Transformers are then used again to step down the voltage to a more suitable level for the consumer. |
| When a current passes through a wire the wire gets hot. The greater the current, the hotter the wire: - what happens when a transformer increases the voltage? | - when a transformer increases the voltage, the current is reduced which means there is less heating effect and therefore less energy is lost to the environment. |
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