A problem by Rahul Kumar

According to Joule's law, the heat loss by a conductor of resistance R when current I passes through it for the time t is: $H = I^{2}Rt$
Now, mathematically if dQ is the amount of heat absorbed by a body of mass m and c is its specific heat capacity then the change in temperature dT is given by: $dT = \frac{dQ}{mc}$
Therefore, the change in heat per minute of the water is actually proportional to the change in temperature per minute and therefore by substituting the values we have; $dT = \frac{I^{2}Rt}{mc}$
or $dT = \frac{7^{2} \times 60 \times 60}{42 \times 4200}$ $dT =\frac{176400}{176400} = \boxed{1}$

We know that Heat=I^2 r t, Here, Heat per minute = 7^2 * 60 * 60=176400 J. It takes one calorie of energy to raise 1 gram of water 1 degree. Water weighs very close to 1 gram per mL. 1 calorie is 4.18 joules.Also, heat = mass *specific heat constant for substance * change in temperature. 176400/4.18(in calories)=42000 * change in temperature change in temp. = 1.004 C