Power (Edexcel IGCSE Physics: Double Science)

• Power is work done per unit time
• Since work done is equal to energy transferred, power is also energy transferred per unit time

• Machines, such as car engines, transfer energy from one energy store to another constantly over a period of time
  • The rate of this energy transfer, or the rate of work done, is power

Power ratings

• Power ratings are given to appliances to show the amount of energy transferred per unit time
• Common power ratings are shown in the table below:

Power ratings table

• 1 kW = 1000 W (1 kilowatt = 1000 watts)
• 1 MW = 1 000 000 W (1 megawatt = 1 million watts)

• Since power is defined as

The rate of doing work

• And work is

Work done = energy transferred

• Then, power can be expressed in equation form as

• Where:
  • W = The work done, measured in joules (J) or newton-metres (Nm)
  • t = time measured in seconds (s)
  • P = power measured in watts (W)

Power, work done and time formula triangle

The formula triangle can be used to rearrange the equation

• For a reminder on how to use formula triangles, see the revision note on Speed