What is power? Power is the rate of using or supplying energy: Power = Energy Power is measured in watts (W) Energy is measured in joules (J) Time is measured in seconds (s) Time Electronics is mostly concerned with small quantities of power, so the power is often measured in milliwatts (mW), 1mW = 0.001W. For example an LED uses about 40mW and a bleeper uses about 100mW, even a lamp such as a torch bulb only uses about 1W. The typical power used in mains electrical circuits is much larger, so this power may be measured in kilowatts (kW), 1kW = 1000W. For example a typical mains lamp uses 60W and a kettle uses about 3kW. Calculating power using current and voltage There are three ways of writing an equation for power, current and voltage: Power = Current × Voltage so P = I × V or I = P V or V = P I where: P = power in watts (W) V = vol...