An immersion heater rated 2.0A; 240V is used to boil water from temperature 52°C to 100°C. If the mass of the water is 2.5kg. determine the time taken to boil the water. [specific heat capacity of water = 4.2 x 10³ jkg−¹ k−¹ ]

A. 1.05 x 10³s
B. 1.05 x 10⁵s
C. 1.05 x 10²s
D. 1.05 x 10⁴s

Correct Answer:

Option A = 1.05 x 10³s

Explanation

Power of heater = lvt = 2 x 240 x t
heat required to boil the water = Mct = 2.5 x 4.2 x 10³ x (100.52) = 2.5 x 4. 2 x 10³ x 48
2 x 240 x t = 2.5 x 4.2 x 10³ x 48
∴ t = (2.5 x 4.2 x 10³ x 48)/2 x 240
= 1050s or 1.05 x 10³3s