Specific Heat and Thermal Conductivity AP Physics 2 FRQ – Exam Style Questions etc.
Specific Heat and Thermal Conductivity AP Physics 2 FRQ
Unit 9: Thermodynamics
Weightage : 15–18%
Exam Style Practice Questions,Specific Heat and Thermal Conductivity AP Physics 2 FRQ
Question
Two containers, each holding a different gas, are brought into thermal contact. The gas atoms in container \(X\) have twice the mass and half the average speed of the gas atoms in container \(Y\). Which of the following best describes the energy transfer by thermal conduction, if any, between the two containers?
(A) There is a net energy transfer from container \(X\) to container \(Y\).
(B) There is a net energy transfer from container \(Y\) to container \(X\).
(C) There is no net energy transfer between the containers, because no atoms move between them.
(D) There is no net energy transfer between the containers, because energy is transferred at approximately equal rates in each direction.
▶️Answer/Explanation
Ans: D
Question
Students design an experiment to determine the thermal conductivity (k) of an unknown substance. A cube of the material to be tested with side area A is clamped to a steam chamber on one side, which maintains a constant
temperature of 100°C, and a block of ice on the other side, which maintains a constant temperature of 0°C, for a difference in temperature from one side to the other of ΔT=100°C. The heat transferred is determined by finding the mass of water melted from ice, \(M_w\), in time t.
(a) Express the thermal conductivity of the substance as a function of the side area of the substance A, the latent heat of fusion of ice \(L_f\) , the mass of the melted water Mw, the time over which the water is collected t, and ΔT.
In ambient conditions, without the steam chamber attached, one gram of water is collected every 10 minutes. With the steam chamber attached, 5 grams of water are melted in 10 minutes. Ice has a latent heat of fusion (latent heat of melting) of \(L_f\) = 334 J/g. The unknown substance has a side length of 10 cm.
(b) Determine the thermal conductivity of the unknown substance.
Answer/Explanation
Ans:
(a) 
(b) \(K=\frac{(4g)(334j/s)}{(0.1m)(600s)(100k)}=0.223 J/s.m.K\)