Electrical Power (AQA GCSE Physics: Combined Science)

• Power is defined as

The rate of energy transfer or the amount of energy transferred per second

• The power of a device depends on:
  • The voltage of the device
  • The current of the device

• The power of an electrical component (or appliance) is given by the equation:

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

Power, current, voltage formula triangle

• The unit of power is the watt (W), which is the same as a joule per second (J/s)

Step 1: List the known quantities

• • Power, P = 48 W
  • Current, I = 4 A

  Step 2: Write down the relevant equation

P = VI

Step 3: Rearrange for potential difference, V

Step 4: Substitute in the values

• The voltage across an electric device depends upon the current and resistance of that device
• Using the equations P = VI with V = IR, power can be written in terms of resistance, R:

Step 1: List the known quantities

• • Resistance, R = 20 Ω
  • Current, I = 6 A

Step 2: Write down the relevant equation 

P = I²R

Step 3: Substitute in the values

P = (6)² × 20 = 720 W