1.3 Electrical Energy

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  • Created by: Twins 1&2
  • Created on: 16-06-13 15:23

3.1 Electrical Appliances

Electrical appliances can transfer electrical energy into useful energy at the flick of a switch.

Uses of everyday electrical appliances include:



Making objects move (using an electric motor)

Creating sound and visual images.

An electrical appliance is designed for a particular purpose and should waste as little energy as possible.

Common electrical appliances include; lamps to produce light energy, speakers to produce sound energy and televisions to produce light and sound energy.

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3.2 Electrical Power

Power is rate of which an appliance transfers energy.

Watt is a unit of power (W)

1 kW(Kilowatts) = 1000W

An appliance with a power of 1 watt transfers 1 joule of energy to another form of energy every second.

You can calculate  power using P=E/t

  • P = power in watts, W
  • E = energy in joules, J
  • t = time taken( in seconds) for energy transfer

Power is energy per second transferred or supplied, so we can write the efficiency equation in term of power: Efficiency = useful power out/total power in (x100%)

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3.3 Using electrical energy

Using electrical energy

The kilowatt-hour is the energy transferred/ supplied  to a 1kW appliance in 1 hour.

E=P x t

E = energy transferred in kilowatt-hours, kWh

P = power of appliance

t = time taken (in hours) for energy to be transferred

Cost of electrical energy supplied is found using the equation:

Total cost= number of kWh used x cost per kWh

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3.4 Cost of effectiveness matters

Cost effectiveness means getting the best value for money.

To compare the cost effectiveness of different appliances, we need  to consider a number of different costs:

  • Buying appliance
  • Installing appliance
  • Running cost
  • Maintenance cost
  • Environmental cost
  • Interest loan on appliance

Many households reduce their energy bill  by installing things like loft insulation and double glazed windows, which are designed to reduce energy wastage.

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3.4 Cost of effectiveness matters


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