Power (Cambridge (CIE) AS Physics): Revision Note

Defining power

• Power is defined as:

  The rate of energy transfer

• Since work done is equal to the energy transferred, power can also be defined as:

  Work done per unit time

• Power can be calculated using the following equations:

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

• 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 power ratings on household appliances, such as 60 W or 1000 W

• These power ratings tell you the amount of energy transferred electrically from the mains supply per second

Solving problems involving power

• Since power describes the energy transferred or the work done per unit time, power calculations commonly include energy or work calculations, which can also include efficiency