Commercial Unit
The commercial unit of electrical energy is kilowatt-hour, written as kWh.
In one line: kWh means power multiplied by hour.
Practice This ConceptUnderstand it
Electricity bills use kWh because home energy use is large and easier to express in this unit. One kWh means using 1 kilowatt of power for 1 hour. It is called one unit in billing language.
Example
Formula and rule
Electrical energy, E = P x t.
1 kWh = 1000 W x 3600 s = 3.6 × 106 J.
See it worked out
Follow the example line by line, then use the same method on new questions.
Worked example
- 1A 2 kW heater runs for 3 hours.
- 2Energy used = 2 × 3 = 6 kWh, so the appliance consumes 6 units.
Method you can reuse
- 1Write power in kW.
- 2Write time in hours.
- 3Multiply power by time to get kWh.
- 4If needed, convert kWh to joules using 3.6 × 106 J per kWh.
Sketch it in your answer
Show a household electricity meter with a kWh reading and a simple appliance label like 2 kW.
Check yourself
Answer the question in your head before opening the answer.
Try it yourself
How many units are used by a 1 kW appliance running for 1 hour?
Think first, then show answerHide answer
Common wrong answer
A common wrong answer is to say kW is the energy unit.
Why it loses marks: KW measures power, not energy.
Don't mix this up
Exam tip
Write it in the exam
Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.
How CBSE asks it
- 1
Enough for 1 mark
The commercial unit of electrical energy is kilowatt-hour, written as kWh.
- 2
Add for 2 marks
Example: A 1 kW heater used for 2 hours consumes 2 kWh, or 2 units.
- 3
Add for 3 marks
Electricity bills use kWh because home energy use is large and easier to express in this unit.
Practice this concept with focused MCQs
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