Units of Measure
Energy

# What is the SI unit of power?

The SI units for mechanical and electrical Power are the Watt

(W), and the Watt (electrical) (We) respectively.

Power is the rate of doing work, or at which energy is

converted. It can be thought of as - "amount of energy used to

perform work, or converted from one form to another, in a specified

period of time, namely, in a second".

The equation is P=W/t, where P is Power, W is the work done and

t is the time taken. The equation, P=E/t, where E is the amount

energy used to do the work, means the same thing. The unit for

Energy is the Joule (J), and the unit for time is the

second (s). The unit of power is then the watt,

which is equal to 1 Joule (J) per second (s).

Electrical Power

There are a few different formulae depending on whether voltage,

current or resistance are being considered. Electrical power is

equal to the amount of current times the voltage, or P=IV.

Electrical power is also equal to the current squared times the

resistance, P=I2R

There are other formulae for the average electrical power of a

sinusoidal voltage, but this is beyond the scope of this

question.

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