Electrical appliances are very useful. The transfer energy into the form we need at the flick of a switch.
Common electrical appliances include:
- lamps...................to produce light
- electric mixers......to produce kinetic energy
- speakers..............to produce sound energy
- televisions............to produce light and sound energy
many electrical appliances transfer energy by heating. this may be useful for a kettle (for example), but energy is often wasted.
Appliances should be designed to waste as little energy as possible.
Power is the rate of energy transfer. The unit of power is the Watt ( W ). An appliance of 1 Watt, transfers 1 joule of electrical energy to another form of energy every second. Often a Watt is too small, so we use kilowatts (KW). 1 Kilowatt = 1000 Watts.
Power is given by the equation:
P = E
P= power (W)
E = energy (J)
T = time taken for energy to be transferred (S)
The efficiency equation can be written in terms of power.
Using Electrical Energy...
- A Kilowatt-hour is the energy supplied to a 1kw appliance in one hour.
- E = P x T
- Total cost = no. of KWh x cost per. KWh
- KWh (kilowatt-hour) is a unit of energy.
The cost of an electricty bill is calculated from the number of units used and measured by a n electricty meter.
E = P x T
E = energy transferred (Kwh)
P = power of appliance (KW)
T = time for energy to be transferred (h - hours )
Electricty meters record the number of KWh of enrgy used.
If the previous reading is subtracted from the current reading, the eletrical energy used between the two readings can be calculated.
Cost of the electrical energy supplied id found using the equation:
Total cost = number of units (KWh) x Cost per unit (KWh)
Cost effectiveness means getting the best for your money. To compare different appliances we need to take account of a number of different costs:
- cost of buying appliance
- cost of installation
- running costs
- maintenance costs
- enviromental costs
- interest charged on loan to buy appliance
Payback time = the time taken for allpliance to pay itself in terms of energy saving.
Cost Effectiveness ...