1. Introduction: What Does the Number on a Bulb Mean?
Look at any bulb in your home. Printed on it is something like "100 W" or "60 W". The fan says something too. The geyser carries a big number like "2000 W". That little "W" is the unit watt, and the number is the electric power of the appliance.
So here is the question this topic answers: what does that number actually measure, and why does the bigger number cost you more on the electricity bill?
You already know two things from before. You know potential difference () — the electric push across the two ends of a device, measured in volt (). And you know current () — the flow of charge through it, measured in ampere (). When current flows through a device, electrical energy gets used up — turned into light, heat, or motion. Electric power is how fast that energy is used — the energy used each second.
By the end, you will be able to say exactly what a "100 W" rating means, work out the power of any appliance three different ways, and read your own home's electricity bill in units.
Stop scrolling. Try it in your head before reading on: two bulbs, "100 W" and "60 W", both glowing. Which one is using up more energy every second?