Power (OCR Gateway GCSE Physics: Combined Science)

• Time is an important consideration when it comes to power
• Two cars transfer the same amount of energy, or do the same amount of work to accelerate over a distance
• If one car has more power, it will transfer that energy, or do that work, in a shorter amount of time

• Two electric motors:
  • lift the same weight
  • by the same height
  • but one motor lifts it faster than the other

• The motor that lifts the weight faster has more power

Two motors with different powers

• 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 is defined as

energy transferred per unit time

• And 

work done = energy transferred

• Therefore, power is also

work done per unit time

• Power can be calculated using the following equation:

• Where:
  • P = power, measured in watts (W)
  • E = energy transferred, measured in joules (J)
  • W = work done, measured in joules (J)
  • t = time, measured in seconds (s)

• This equation can be rearranged with the help of a formula triangle:

Work, power, time formula triangle