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Electricity and Magnetism

Electrical Power and Energy

Any component which possesses resistance will convert electrical energy into thermal energy.

Consider the simple circuit shown below.

The current, I, is a measure of the number of Coulombs of charge which pass through the resistor per second.

The voltage, V, is a measure of the number of Joules of energy lost by each Coulomb of charge passing through the resistor.

Therefore, the number of Joules of energy converted to heat by the resistor per second is given by

energy per second = voltageŚcurrent

and energy per second is power.

So,

P = VI

To calculate the quantity of energy converted to heat, w, in t seconds we have

w = VIt

and combining this result with the definition of resistance we have

w = I2Rt

w = (V2/R)t

 

© David Hoult 2008