Power (CIE A Level Physics)

• The power of a machine is the rate at which it transfers energy
• Since work done is equal to the energy transferred, power can also be defined as the rate of doing work or the work done per unit time

$P =\frac{ E}{t} =\frac{ W}{t}$

• Where:
  • P = power in watts (W)
  • E = energy in joules (J)
  • W = work done in joules (J) or newton metres (N m)
  • t = time in seconds (s)

• You may be familiar with labels on lightbulbs which indicate their power such as 60 W or 100 W
• These power ratings tell you about energy transferred electrically rather than mechanically and so will require a different equation