Electrical Power and Energy

When a direct current of I amperes is flowing in an electric circuit and the voltage across the circuit is V volts, then

power, in watts P =VI
Electrical energy = Power × time
= VIt joules

Although the unit of energy is the joule, when dealing with large amounts of energy, the unit used is the kilowatt hour (kWh) where

1 kWh = 1000 watt hour
= 1000 × 3600 watt seconds or joules
= 3 600 000 J

A source e.m.f of 5V supplies a current of 3A for 10 minutes. How much energy is provided in this time?

Energy = power × time, and power = voltage × current. Hence
Energy = VIt = 5 × 3 × (10 × 60)
= 9000 Ws or J = 9 kJ

Read More Topics
Electrical potential and e.m.f
Resistance and conductance
Secondary standard of emf
Primary source of electrical power

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Santhakumar Raja

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