The Power Equation
Electric power is the rate at which energy is converted from electrical engery to some other form
such as heat or mechanical energy. When charge moves through a reisistor it loses potential energy.
That energy is converted to heat. Power dissipated (as heat) by a component in a DC circuit is given
by the product of the voltage across the component and the current through the component:
Watts = Volts * Amps
OR
P = V* I
since V = I * R, by substitution,
P = I2 * R and P = V2
R

For example, in the circuit below, how much power is dissipated in the 1.5 ohm resistor?
Solving for current first: I = V/R = 1.5/1.5 = 1
therefore,
P = 1.5 * 1 = 1.5 Watts
alternatively,
P = I2 * R, so
P = 1 * 1* 1.5 = 1.5 Watts
In each case the power is dissipated as heat in the resistor. Resistors can only dissipate power.
They convert electrical energy to heat.

heat dissipated

R1 1.5

+

Zap-O-Matic
Battery
1.5V

I

Since the resistor dissipated 1.5 watts of power, the batter must have supplied 1.5 Watts of power.
We can also say that the battery dissipated -1.5 Watts.

Dissipation
conversion of electrical
energy to heat

is

the

opposite

of

Generation
conversion of some other type
of energy to electrical energy

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