Electricity from First Principles
Power & Energy
12 min · 2 worked examples · 3 questionsFree
Why components have wattage ratings, and how to check you are inside them.
After this lesson you can
- Choose the right power formula for what you know
- Work out whether a resistor will get too hot
- Convert between watts, joules and time
Power is the rate of energy transfer
Energy is measured in joules. Power is how quickly that energy is transferred, measured in watts, where one watt is one joule per second.
P = E ÷ t
In electrical terms there is a much more convenient form. Voltage is energy per charge and current is charge per second, so multiplying them gives energy per second, which is power:
P = V × I
That is why a component running at 5 V and drawing 2 A dissipates 10 W.
In the full lesson
- Power is the rate of energy transfer
- Three forms of the same equation
- Component ratings
- Energy and what it costs
Free with an account. Read it, work the examples, answer the questions, then build it in the simulator.