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
Verified Correct Answer: A.
Physical Principles & Numerical Solution
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 103s
Source: Myschool Past Questions Archive (Record #13843)