Question

1.
5. An electric kettle market 1 kW, 230V, takes 7.5 minutes
to bring 1 kg of water at 15°C to boiling point. Find the
efficiency of the kettle.
(Ans : 79.07%)

​

Answer 1

The efficiency of the kettle is 79 %.

Explanation:

We are given that:

• Power of electric kettle = 1 kW
• The voltage of electric kettle = 230 V
• Time taken by kettle to raise the boiling point of water  = 7.5 minutes  
• Mass of water = 1 Kg
• To Find: The efficiency of electric kettle = ?

Solution:

Heat produced = V x I x t = Pt

Heat produced = 1000 W x 7.5 x 60

Heat absorbed = 1 x 4200 (100 - 15)  = 4200 x 85

Efficiency = Heat absorbed / heat produced x 100

                = 4.2 x 85 x 10^3 / 4.5 x 10^5 x 100

                = 357 / 4.5 = 79 %