Question

A thermos flask contains milk . Will there by any change in temperature of the milk , if the flask is shaken rapidly . Has heat been added to it and internal energy change? Explain

Answer 1

Answer:

Explanation:

a) Yes, its temperature rises. Since the thermos bottle is vigorously shaken, the kinetic energy of molecules in the milk will be increased. As the temperature is directly proportional to the average kinetic energy of the molecule, therefore temperature of the milk will be increased.

(b) No, heat has been added to the milk.A thermos bottle contains milk, but as the thermos bottle is insulated from its surrounding, therefore ΔQ = 0. Thus, heat has not been added to the milk. So the sign of the work done will be negative.

(c) Yes, work has been done on the system as heat is added to the milk. As, the thermos bottle is vigorously shaken, therefore work is done on the milk which is against the viscous force.

(d) Yes, its internal energy has changed.Heat is the part of internal energy which is transferred from one body to another an account of the temperature difference. So the internal energy of a body was acquired by heat transfer.

In accordance to the first law of thermodynamics, ΔQ = ΔU + ΔW. From the above discussion, as, ΔQ = 0 and the sign of the work done will be negative, therefore ΔU should be positive. Thus internal energy of the milkwill be increased.