Electrical appliances transfer electrical energy into whatever form of energy we need at the flick of a switch.
eg. lamps (to produce light), speakers (to produce sound energy) and televisions (to produce light and sound energy).
Many electrical appliances transfer energy by heating. This may be a useful transfer (eg. In a kettle) but energy is often wasted.
The power of an appliance is the rate at which it transfers energy and it is measured in Watts (W).
An appliance with a power of 1W transfers 1Joule of energy to other forms of energy every second.
Often a watt is too small a unit to be useful, so power may be given in kilowatts (kW).
!!! 1 kW = 1000 W !!!
P = E / t
t=time taken for energy to be transferred (secs)
Effeciency = useful power out
total power in
Using electrical energy
Kilowatt-hour is used instead of Joules when large numbers are used when measuring the amount of electrical energy used.
A kilowatt-hour is the amount of energy that is transferred by one kilowatt appliance when used for one hour.
The amount of energy transferred to a mains appliance can be found using:
E = P x t
E=energy transferred in kWh
P=power of the appliance (kW)
t=time taken for the enrgy to be transferred (hours)
The cost of electrical energy supplied is found using the equation:
Total cost = number of kWh x cost per kWh
Cost effectiveness means getting the best value for money.
To compare the cost effectiveness of different appliances, we need to take account of a number of different costs. These may include the maintanance, environmental and running costs.
To reduce energy bills, you may buy newer, more effecient appliances (like a new fridge) and install materials designed to reduce energy wastage (such as loft insulation).
The payback time is the time it takes for an appliance or installation to pay for itself in terms of energy savings.
payback time (years) = cost of installation (£) ÷ savings per year in fuel costs (£)