1.3 Electrical Energy

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

Uses of everyday electrical appliances include:

Heating

Lighting

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.

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%)

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

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.