A) the sphere reaches at room temperature in the last
B) the cube reaches at room temperature in the last
C) the circular plate reaches at room temperature in the last
D) all will reach the room temperature simultaneously
Correct Answer: A
Solution :
Rate of flow of heat given by \[\frac{Q}{t}=KA.\frac{{{\theta }_{1}}-{{\theta }_{2}}}{l}\] where K is coefficient of thermal conductivity A the area, \[({{\theta }_{1}}-{{\theta }_{2}})\]temperature difference, \[l\] (the length. Since, surface area A of a sphere is minimum and time (t) \[t\propto \frac{1}{A}\] Hence, sphere will take maximum time in cooling.
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