What is Watt?

What is Watt?

The watt is an SI unit of Power. It is used to indicate the rate at which the energy spent in the form of ration, absorption or dissipation. In an electric circuit, One watt is defined as the current flow of one ampere with the voltage of one volt. Also, One watt can be defined as one joule per sec, Hence the ratio between the energy and the time can be called as watt.

1W = 1 J / 1s

Also, the power unit is mentioned in the short form of the English capital letter “W”.

Watt in a DC electric circuit can be calculated by the product of Amps and Volts. Let as assuming a resistance in ohm, whose Power in W, the voltage in volts and current in Amps,

The watt will be

Watt = Volts * Amps

W = V / I


W = Amp2 * Ohms

Hence power is directly proportional to the current, voltage and resistance of the circuit.

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But in the AC circuit, the electric has additional parameter is called reactance (X). The reactance involved circuit current opposing parameter is called impedance.

Impedance (Z) is the vector sum of resistance and reactance. Therefore

Watt = Current2 * (R + j X) = Current2 * Impedance


W = Amp2 * Ohms

Also, you can see power unit Watt can be mentioned in different form such as

  • nW – Nano- Watt (10-9) it is used to indicate the power loss in the Integrated circuit
  • µW – micro Watt (10-6) it is used to indicate the power consumption in the Integrated circuit
  • mW – milli Watt (10-3), it is used to indicate the power rating of the passive components
  • W – Watt (10), it is used to indicate the power rating of the commercial appliances
  • kW – kiloWatt (103), used to indicate the motors, industrial equipment
  • MW – Mega Watt (106) and it is used to indicate the rating of Alternator, Transformers etc
  • GW – Giga Watt (109) and it is used to indicate the transmission lines rating.
  • dBmW & dBW (sometimes dBmW or decibel-milliwatts) used to indicate power capability of fibre-optical communication networks
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