# Physics P1 3.3 Using electrical energy.

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What is the kilowatt-hour?
Te energy supplied to a 1 kW appliance in 1 hour.
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How do companies that supply mains electricity know what to charge customers?
They charge customers for the amount of electrical energy that the customer uses.
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Why isn't the joule a suitable unit for companies to use to measure electrical usage?
Because of the large numbers involved, therefore the amount of energy used is measured in kilowatt-hour (kW h).
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What is a kilowatt-hour?
It is the amount of energy that is transferred by a one-kilowatt appliance when used for one hour.
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How can the amount of energy transferred to a mains appliance be found?
Using the equation E = P x t.
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What does the E mean in the equation E = P x t?
E is the energy transferred in kilowatt-hours (kWh).
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What does the P mean in the equation E = P x t?
P is the power of the appliance in kW.
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What does the t mean in the equation E = P x t?
t is the time taken (in hours) for the energy to be transferred.
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What does the electricity meter in a house record?
The number of kWh of energy used. If the previous meter reading is subtracted from the current reading the electrical energy used between the readings can be calculated.
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What equation is used to find the cost of the electrical energy supplied?
Total cost = number of kWh x cost per kWh.
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Where should the cost per kWh be found?
On the electricity bill.
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How much electrical energy, in kWh, is transferred when a 9kW shower is used for 15 minutes?
2.25 kWh.
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The price of 1 kWh of electrical energy is 9p. How much does it cost to use a 60W electric light for 4 hours?
2.16p.
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**REMEMBER THAT THE KILOWATT-HOUR IS A UNIT OF ENERGY**
**
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## Other cards in this set

### Card 2

#### Front

How do companies that supply mains electricity know what to charge customers?

#### Back

They charge customers for the amount of electrical energy that the customer uses.

### Card 3

#### Front

Why isn't the joule a suitable unit for companies to use to measure electrical usage?

### Card 4

#### Front

What is a kilowatt-hour?

### Card 5

#### Front

How can the amount of energy transferred to a mains appliance be found?