Monday, March 8, 2010

Electric power


When an electrical appliance is switched on, the current flows and the electrical energy supplied by the source is transformed to other forms of energy (e.g heat and light energy in electric bulb)
Therefore, we can define electrical energy as :
The energy carried by electrical charges which can be transformed to other forms of energy by the operation of an electrical appliance.


Electric power: rate of transferring electric energy


P = E /t

where P = power [Watt]
E = electric energy used / dissipated [Joule]
t = time [seconds]

P = IV

where P = power [Watt]
I = current [Ampere]
V = potential difference [Volt]

From P = IV and V = IR,
P = I2 R
P = V2 /R


Electrical appliances are usually labeled by its voltage and power rating
Voltage – required potential difference to operate the appliance
Power rating – energy dissipated by the appliance when the correct voltage is supplied

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