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How to Get the Power Dissipated

Every element in a circuit (such as a power supply, resistors, inductors, etc.) either supplies power to the rest of the circuit or dissipates power supplied by some other element. For most circuit elements, you can calculate the power dissipated by multiplying the voltage across that element by the current running through it, giving you the equation P = V x I. However, there is more to calculating power than that. You must also carefully track the polarity of the voltage and the direction of the current to make sure that element is dissipating power instead of supplying it.

Instructions

- 1
  Find the voltage across your circuit element. If it is not a resistor, pay attention to the polarity of the voltage.
- 2
  Find the current through your element. If it isn't a resistor, note whether the current enters the positive terminal or the negative terminal. If current enters through the positive terminal, the current is positive. If not, the current is negative.
- 3
  Check your units for the voltage and current found in steps 1 and 2. Voltage should be in volts. Current should be in amperes. Convert them if necessary. For example, you should write 1.2kV (kilovolts) as 1200V (volts).
- 4
  Multiply voltage by current. Their product is the power dissipated or supplied, in units of watts. Ensure that you use the sign convention for current outlined in step 2. If their product is positive, that circuit element dissipates power. If negative, that element supplies power. For example, an element that measures 14V across and 2A into the positive terminal dissipates 28W (watts) of power.

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