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# Electrical Potential difference & mechanical work – Numerical problems

Last updated on August 25th, 2023 at 01:22 pm

In this post, we will solve numerical problems based on the formula of electric potential difference and mechanical work.

Formulas Used

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:

Electrical potential difference =electrical energy converted into other forms/amount of 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?

Solutions

See also  An electric heater of power 600 W raises the temperature of 4.0 kg of a liquid from 10 C to 15 C in 100 s. Calculate: (i) the heat capacity of 4.0 kg of liquid
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