AQA GCSE Physics

Revision Notes

2.3.3 Calculating Energy Transfers

Calculating Energy Transfers

  • Work is done when charge flows through a circuit
    • Work done is equal to the energy transferred
  • The amount of energy transferred by electrical work in a component (or appliance) depends upon:
    • The current, I
    • The potential difference, V
    • The amount of time the component is used for, t
  • When charge flows through a resistor, for example, the energy transferred is what makes the resistor hot
  • The energy transferred can be calculated using the equation:

E = P × t

  • Where:
    • E = energy transferred in joules (J)
    • P = power in watts (W)
    • = time in seconds (s)
  • Since P = IV, this equation can also be written as:

E = I × V × t

  • Where:
    • I = current in amperes (A)
    • V = potential difference in volts (V)
  • The electrical energy transferred also depends on the charge and potential difference:

E = Q × V

  • Where:
    • Q = charge in coulombs (C)
    • V = potential difference in volts (V)
  • When charge flows around a circuit for a given time, the energy supplied by the battery is equal to the energy transferred to all the components in the circuit
  • These can be rearranged using the following formula triangles:

Energy, charge, potential different formula triangle

Energy, power, time formula triangle

Worked Example

Calculate the energy transferred in 1 minute when a current of 0.7 A passes through a potential difference of 4 V.

Step 1: Write down the known quantities

    • Time, t = 1 minute = 60 s
    • Current, I = 0.7 A
    • Potential difference, V = 4 V

Step 2: Write down the relevant equation

E = I × V × t

Step 3: Substitute in the values

E = 0.7 × 4 × 60 = 168 J

Exam Tip

‘Energy transferred’ and ‘work done’ are often used interchangeably in equations, for example in the previous topic on Power

Always remember that the time t in the above equations must always be converted into seconds

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