How long can a 100w bulb burn on one unit of electricity?

This is a straightforward but frequently asked numerical question in competitive exams. The relationship between energy, power, and time is given by the simple formula Energy = Power × Time. One unit of electricity equals 1 kilowatt hour (kWh), which means 1000 watts consumed for 1 hour. A 100W bulb consumes only 100 watts, so dividing 1000W by 100W gives us exactly 10 hours — meaning a 100W bulb can burn continuously for 10 hours on just one unit of electricity.

• Formula: Time = Energy ÷ Power = 1000 Wh ÷ 100 W = 10 hours
• One Unit of Electricity: 1 kWh = 1000 Watt-hour — this is the standard unit used for measuring household electricity consumption
• Calculation: 1 kWh ÷ 100W = 10 hours — simple division gives the answer directly
• Practical Significance: This calculation helps understand electricity bills — running a 100W bulb for 10 hours costs exactly one unit of electricity
• Energy Saving: Replacing a 100W bulb with a 10W LED gives the same light but runs for 100 hours on just one unit — ten times more efficient