DC Fundamentals Unit 10 – Power in DC Circuits
Unit 10 – Power in DC Circuits ..................................................................................................
UNIT OBJECTIVE
At the completion of this unit, you will be able to determine power in series, parallel, and
series/parallel resistive circuits.
UNIT FUNDAMENTALS
Electric power is the rate of doing work per unit time. The unit of power measurement is the
watt (W). 1W of power equals the work done in 1 second by 1V of potential difference in
moving 1C (electron flow) of charge.
1C of charge per second is 1A of current flow. Therefore, power in watts can be defined as the
product of voltage and current: P = E x I. In a resistor, power (E x I) dissipates in the form of
heat.
Ohm's law may be modified to accommodate the relationship between power, voltage, and
current.
Power is also related to the square of current or voltage.
P = E x I P = E x I
= I x R x I = E x E/R
= I^2 x R = E^2 /R