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).
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
There are other formulae for the average electrical power of a
sinusoidal voltage, but this is beyond the scope of this