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Commercial Unit

The commercial unit of electrical energy is kilowatt-hour, written as kWh.

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Student-friendly explanation

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.

How to write this in exams

  1. 1

    Start with the exact idea

    The commercial unit of electrical energy is kilowatt-hour, written as kWh.

  2. 2

    Then show how to use it

    1. Write power in kW. 2. Write time in hours. 3. Multiply power by time to get kWh. 4. If needed, convert kWh to joules using 3.6 x 10^6 J per kWh.

  3. 3

    Add one concrete example

    A 1 kW heater used for 2 hours consumes 2 kWh, or 2 units.

  4. 4

    Avoid this incomplete answer

    A common wrong answer is to say kW is the energy unit. That is wrong because kW measures power, not energy.

Definition

The commercial unit of electrical energy is kilowatt-hour, written as kWh.

Example

A 1 kW heater used for 2 hours consumes 2 kWh, or 2 units.

Rule to remember

Electrical energy, E = P x t. 1 kWh = 1000 W x 3600 s = 3.6 x 10^6 J.

Memory hook

kWh means power multiplied by hour.

Examples and method

Worked example

A 2 kW heater runs for 3 hours. Energy used = 2 x 3 = 6 kWh, so the appliance consumes 6 units.

Method to apply

1. Write power in kW. 2. Write time in hours. 3. Multiply power by time to get kWh. 4. If needed, convert kWh to joules using 3.6 x 10^6 J per kWh.

Diagram support

Show a household electricity meter with a kWh reading and a simple appliance label like 2 kW.

How CBSE asks it

Usually asked in billing numericals, unit conversion questions, or short questions about why households use kWh.

Avoid common mistakes

Common confusion

Students often confuse kWh with kW and forget that time must be included.

Common wrong answer

A common wrong answer is to say kW is the energy unit. That is wrong because kW measures power, not energy.

Exam tip

Convert power and time carefully before finding units consumed in billing questions.

Quick check

How many units are used by a 1 kW appliance running for 1 hour?

It uses 1 unit because 1 kilowatt for 1 hour is exactly 1 kilowatt-hour.

Answer writing and exam use

1-mark answer

The commercial unit of electrical energy is kilowatt-hour, written as kWh.

2-mark answer

The commercial unit of electrical energy is kilowatt-hour, written as kWh. Electrical energy, E = P x t. 1 kWh = 1000 W x 3600 s = 3.6 x 10^6 J. A 1 kW heater used for 2 hours consumes 2 kWh, or 2 units.

3-mark answer

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. Electrical energy, E = P x t. 1 kWh = 1000 W x 3600 s = 3.6 x 10^6 J. A 2 kW heater runs for 3 hours. Energy used = 2 x 3 = 6 kWh, so the appliance consumes 6 units. Usually asked in billing numericals, unit conversion questions, or short questions about why households use kWh. A common wrong answer is to say kW is the energy unit. That is wrong because kW measures power, not energy.
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