MCQ Detailed View

Electricity consumption in households is measured in terms of energy used over time. The standard unit for this measurement is the kilowatt-hour (kWh).

A watt (W) is the unit of power, equal to one joule per second. A kilowatt (kW) is equal to 1000 watts. When an electrical appliance operates, it consumes energy depending on its power rating and the time it is used.

For example:

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  If you run a 1 kW electric heater for 1 hour, it consumes 1 kWh of energy.

  
  


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  If you run a 100 W bulb for 10 hours, it consumes 1 kWh of energy as well (because 100 W × 10 h = 1000 Wh = 1 kWh).

  
  

Let’s analyze the options:

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  Watt-hour: This is a smaller unit of energy, but electricity bills are not measured in watt-hours.

  
  


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  Joule-hour: Not a standard unit; energy is measured in joules, but combining joules with hours is not conventional.

  
  


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  Kilowatt-hour: ✅ Correct, and this is the standard commercial unit of electricity billing worldwide.

  
  


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  Kilojoule-hour: Again, not a standard unit in practice.

  
  

A kilowatt-hour can also be converted into joules for scientific calculations:

1 kWh=1000 W×3600 s=3.6×106 J1 \text{ kWh} = 1000 \text{ W} \times 3600 \text{ s} = 3.6 \times 10^6 \text{ J}1 kWh=1000 W×3600 s=3.6×106 J

This shows that kWh is simply a larger, practical unit for expressing large amounts of energy consumption conveniently, rather than dealing with millions of joules.

In real life, electric companies charge customers based on kWh. For example, if the tariff is Rs. 30 per kWh, and your household consumes 300 kWh in a month, your electricity bill will be Rs. 9000 (excluding other charges).

Thus, the kilowatt-hour (kWh) is the correct and practical unit for home electricity energy consumption.