Define kilowatt-hour (kWh). What is its relation with joule? How can you calculate energy in kWh by a formula? - Students Free Notes

Define kilowatt-hour (kWh). What is its relation with joule? How can you calculate energy in kWh by a formula?

Kilowatt-Hour (kWh)

A kilowatt-hour (kWh) is a unit of energy that is commonly used to measure electrical energy consumption. It represents the amount of energy consumed by a device with a power rating of 1 kilowatt (kW) operating for 1 hour.

In simpler terms, 1 kWh is the energy used when a 1,000-watt device runs for one hour.

Relation Between Kilowatt-Hour (kWh) and Joule (J)

The joule (J) is the SI unit of energy, and the kilowatt-hour (kWh) is a larger unit used in the context of electrical energy, commonly in household or industrial settings.

To convert kilowatt-hours to joules, we use the following relationship:

1 kWh=1 kW×1 hour

Since:

  • 1 kW=1,000 W
  • 1 hour=3,600 seconds

Therefore:

1 kWh=1,000 W×3,600 s=3,600,000 J

Thus,

1 kWh=3.6×106 J

How to Calculate Energy in kWh

To calculate energy in kilowatt-hours (kWh), you can use the formula:

Energy (kWh)=Power (W)×Time (hours)/1,000

Where:

  • Power (W) is the power of the device in watts (W).
  • Time (hours) is the duration of usage in hours.

Example:

If you have a device with a power consumption of 500 watts and it runs for 3 hours, the energy consumed in kWh is:

Energy (kWh)=500 W×3 hours/1,000=1.5 kWh

This means the device consumes 1.5 kWh of energy in 3 hours.

Summary:

  • Kilowatt-hour (kWh) is a unit of energy, primarily used to measure electricity consumption.
  • 1 kWh = 3.6 million joules (3.6 × 10⁶ J).
  • The energy consumed in kWh can be calculated by the formula: Energy (kWh)=Power (W)×Time (hours)/1,000