Concepts Of Physics MCQ Edition [Volume 2]PhysicsCalorimetry
Determine the time required to heat 20 kg of water from 10^ C to 35^ C using an immersion heater rated at 1000 W . Assume that 80 % of the power input is utilized to heat the water. Specific heat capacity of water = 4200 J kg ⁻¹ K ⁻¹ .
Options
- A28 min
- B35 min
- C43.75 min
- D61.25 min
Correct answer
C. 43.75 min
Step-by-step solution
The heat required to raise the temperature of the water is given by: Q = mc T Substituting the given values: Q = 20 4200 (35 - 10) Q = 20 4200 25 = 2100000 J The useful power utilized to heat the water is 80 % of the rated power: P_ useful = 80 100 1000 = 800 W The time t required to heat the water is: t = Q P_ useful = 2100000 800 = 2625 s Converting the time into minutes: t = 2625 60 min = 43.75 min