Energy & Power (Edexcel GCSE Physics: Combined Science)

• Power is defined as the energy transferred per second
  • Power is measured in watts

• Since power is energy transferred per second, the watt can also be defined as 1 joule per second

1 W = 1 J / s 

• 1 kilowatt (1 kW) is equal to 1000 watts, or 1000 joules of energy transferred per second (1 kJ / s)

• Power is defined as the energy transferred per unit time:

• Power can also be defined as the work done per unit time:

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

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

Work, power, time formula triangle

Step 1: List the known values

• • Power, P = 2000 W
  • Time, t = 5 minutes = 5 × 60 = 300 s

Step 2: Write down the relevant equation 

Step 3: Rearrange for energy transferred, E

Energy transferred = power × time

E = Pt

Step 4: Substitute in the values

E = 2000 × 300 = 600 000 J