Concept preview

What you will be able to do

1. 01Calculate electrical power with $P = IV$ and its variants
2. 02Relate power, energy and time
3. 03Compute the cost of electrical energy in kilowatt-hours

Power is how fast energy is transferred, $P = \dfrac{E}{t}$, measured in watts (W), where one watt is one joule per second. In a circuit, every coulomb of charge carries energy $V$ (the voltage), and $I$ coulombs pass each second — so the energy delivered per second is current times voltage: $P = IV$. A $60\ \text{W}$ bulb converts $60$ joules of electrical energy into light and heat every single second.