Question

Calculate the time taken by an immersion heater, which supplies energy at the rate of 7000 J/minute to raise temp. of 5 kg water from 22°C to 47°C.

Answer 1

`"Q"/"t"` = 7000 J/min

m = 5 kg

ΔT = 47 - 22 = 25°C

C = 4200 J/kg°C 

Q = m x C x T

    = 5 x 4200 x 25 = 525000 J

Time taken = `525000/7000` = 75 min