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5.2.3 Electrical Power

By the end of this lesson you can:

  • Calculate power using P = VI
  • Calculate the energy used by an appliance
  • Compare the power ratings of devices
Find your course: NSW Year 11: Electric circuitsNSW Year 12QLD Unit 1: Electrical circuitsVIC Unit 1: Electricity and energyAP Physics 2: Unit 11IB: B.5 Current and circuits
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Learn the idea: a short explanation, then a check.

In an earlier lesson, we introduced power as the rate at which energy is transformed or transferred over time (P = ΔE⁄t). When applied to electric circuits, power measures how rapidly electrical potential energy is converted into other useful forms of energy—such as light, heat, or mechanical work.

Theoretical Overview

In any electric circuit, potential difference (V) represents the energy transformed per unit of charge (V = ΔE⁄Q), while electric current (I) represents the rate of charge flow (I = Q⁄t). Combining these concepts yields the fundamental formula for electrical power:

P = VI

Where:

  • P is power in watts (W, or Joules per second, J/s)
  • V is potential difference/voltage in volts (V)
  • I is current in amperes (A)

By applying Ohm's Law (V = IR), we can also express power in terms of resistance (R):

  • P = I2R (useful for components connected in series)
  • P = V2⁄R (useful for components connected in parallel)

This video explores electrical power in action, reviews these essential mathematical principles, and compares how power is distributed across series and parallel circuit configurations.

 
Our homes are connect in parallel circuits.
So how does the electricity supply company determine how much power we use?
In essence the determine the amount of energy by determining the amount of current drawn at any one time by our home

This video examines how this works and why the unit for our usage is the kilowatt hour