Question

Two objects, A and B, at initial temperatures TA and TB are placed into thermal contact. If TA > TB, cA > cB, and mA > mB, why is the equilibrium temperature of both objects closer to TA than TB?

a) Less heat flows out of object A than flows into object B, and so TA changes less than TB changes

b) The same amount of heat flows out of A as flows into B, but it takes more heat energy to change the temperature of A because of A’s larger thermal mass.

c) Because its specific heat is higher, more heat flows out of A than into B, and this changes the temperature of B more than A.

d) Since A is hotter and more massive than B, heat flows out of A and into B until the temperature of B is raised to TA. The temperature of A remains constant.

e) Heat flows out of B and into A because this is the direction of the temperature gradient, which changes the temperature of B more than A.

An explanation for the answer would be great!!

Answer 1

Answer : (b)

" The same amount of heat flows out of A as flows into B, but it takes more heat energy to change the temperature of A because of A’s larger thermal mass."

Object (A) and (B) are placed in contact with each other. Since TA > TB, heat flows from (A) to (B). The amount of heat lost by (A) will be equal to heat gained by (B). Heat flow is same. [from the above explanation it is clear that options(a),(c) and (e) are wrong]

Since heat is lost by object (A), there will be a change in temperature of object (A). [from the above explanation it is clear that options (d) is wrong]

Since object (A) has more mass and more specific heat than object (B), more heat has to be lost to decrease its temperature or more heat is required to increase its temperature than compared to B.

Example : More heat is required for A to change its temperature from 20 Celsius to 40 Celsius than B. Because it has more specific heat and mass.