Solution:
According to the question, we have –
Specific heat capacity (c) of the material is 960 J kg-1 K-1
Change in temperature becomes
△T = (38 – 18)0 C = 200 C
or, △T = 20 K (temperature difference will remain 20 no matter what)
Power (P) of heater is 500 W
We know that the expression for heat energy is ==> △Q = mc△T
Upon substituting values, we have ==> △Q = 50 × 960 × 20
Then the time taken by a heater to raise the temperature of material can be determined as follows –
t = △Q / P
putting known values, t = (50 × 960 × 20) / 500
Thus, t = 1920 seconds
Or, t = 32 minutes