The potential difference between two points in a circuit is the electrical energy per unit charge. When this electrical energy is converted into other forms of energy (thermal, light, mechanical, etc.), then it can be expressed as:

**potential difference =electrical energy converted into other forms/charge passing**or, potential difference =work done/charge passing [as energy is the result of doing work, W ]

=> **V = W/Q**

## Numerical problems based on Electrical Potential difference & mechanical work done

**1) The element of an electric kettle that takes a current of 12.5 A produces 540 kJ of thermal energy in 3 minutes.**

a) How much charge passes through the element in these 3 minutes?

b) What is the potential difference across the ends of the element?

**2) A 12 V pump for a fountain in a garden pond can pump water up to a height of 0.80 m at a rate of 4.8 litres per minute.**

a) How much work does the pump do per minute when raising the water to a height of 0.80 m? (You may assume that one litre of water has a mass of 1 kg.)

b) If the pump is 75% efficient, how much charge passes through the pump motor in one minute?

c) What current does the motor take when operating under these conditions?