Electrical Energy & Power (AQA A Level Physics)

Energy & Power

• In mechanics, power P is defined as the rate of doing work

  • The potential difference is the work done per unit charge

  • Current is the rate of flow of charge

• Therefore, the electrical power is defined as the rate of change of work done:

• The work done is the energy transferred so the power is the energy transferred per second in an electrical component

• The power dissipated (produced) by an electrical device can also be written as

• Using Ohm's Law V = IR to rearrange for either V or I and substituting into the power equation, means power can be written in terms of resistance R

• This means for a given resistor if the current or voltage doubles the power will be four times as great.

  • Which equation to use will depend on whether the value of current or voltage has been given in the question

• Rearranging the energy and power equation, the energy can be written as:

E = VIt

• Where:

  • E = energy transferred (J)

  • V = voltage (V)

  • I = current (A)

  • t = time (s)