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Electric Power and Energy

The electric power P consumed by an electrical device is the product between the voltage V at the terminals (in Volts) and current I passing through it (in amps):
P = V × I

The unit of power is the Watt (W).

  • For direct current, P = V × I
  • For alternating current used with resistance type components (lamps, heaters), P = VRMS × IRMS where  VRMS and IRMS are the RMS values of voltage and current.

The electrical energie consumed by an electrical appliance is the product of electrical power (P) and the duration of time used (t)

E = P × t

The unit of energy is the Joule (J). Another frequently used unit is the Watt-hour (Wh). Look at your home electricity bill.

1 Wh = 3600 J

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