Calculating Energy Transfers (OCR Gateway GCSE Physics: Combined Science)

• 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)
  • t = 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

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