Measuring Energy (Work) & Power


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ENERGY

The basic unit of energy is the joule (J), named in honour of James Prescott Joule, one of the pioneering physicists to explore the properties of mechanical energy and heat.

When a force of 1 newton (1N) moves an object 1 metre (1m) the amount of work done is exactly one joule (1J).

Energy is measured in units called joules (J) .


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POWER

The basic unit of power is the watt (W), named in honour of James Watt, the developer of the first modern steam engine.

The rate at which energy is transferred is measured in watts (W), where a watt is one joule per second.

Purchasing Energy

Most of our electrical appliances and lighting fixtures are rated according to the power that they dissipate. For example, a common light bulb is rated at 60 watts (60W). This means it dissipates 60 joules (60J) of energy (mostly as heat) every second.

The electrical utility company charges us by the amount of power that our appliances dissipate and according to the length of time that the power is used.

The basic unit of energy that the electrical utility company measures is the kilowatt-hour.

A kilowatt is 1000J/s and one hour is 3600s. Hence 1kWh = 3.6 MJ.

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