# 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

### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
Close