Physics 73 Review

Physics 73 Thermodynamics Review

September 15, 2016

Lecturer: Lectur er: Regin Reginald ald Christian S. Berna Bernardo rdo

ERM. In the ERM shown,

> T C . Which of the process shown violates the 2nd Law of thermodynamics?

(a) I only (b) II and III only (c) I and III only (d) I, II and III

Lecturer: Reginald Christian S. Bernardo

T H

Power Ref. A refrigerator has a coefficient of performance of 3.5.

If it uses 200 W of electrical power, how much heat is delivered to the hot reservoir in one second? (a) 57 J (b) 200J (c) 700J (d) 900J


Reverse Psychology. A heat engine has an efficiency of 25%. If it

is to be run in reverse as a refrigerator, what is the corresponding coefficient of performance? (a) 0.75 (b) 1.33 (c) 3.00 (d) 4.00


The More the Merrier. A heat engine has an efficiency of 25%.

A refrigerator with coefficient of performance 4 is used in conjunction with this heat engine to increase efficiency. What is the resulting efficiency of the combination if 40% of the work done by the heat engine is used to power the refrigerator? (a) 0.300 (b) 0.450 (c) 0.500 (d) 0.625


The Perfect Steam. A steam engine works between a hot

reservoir at 373 K and a cold reservoir at 273 K. What is the maximum possible work that it can do if 200 J of energy is extracted from the hot reservoir? (a) 53.6 J (b) 73.3 J (c) 146.4 J (d) 273.0 J


If I Lose Myself. A glass filled with 0.500 kg ice initially at 0

◦

C

is allowed to completely melt and reach the room temperature 20 C. Assuming during this process, the room does not change its temperature, what is the total change of entropy of the room and the ice? ◦

(a) 46.8 J/K (b) 463.3 J/K (c) 759.4 J/K (d) 1472 J/K


Into entropy. Which of the following is true about entropy?

(a) It can be negative. (b) It doubles when the number of microstates is doubled. (c) It is smallest for the most probable macrostate. (d) It is smallest for the macrostate with the least number of microstates.


Triple. The number of microstates of a gas is proportional to V3 ,

where V is the volume that the gas occupies. What is the change in entropy per molecule of the gas if the volume it occupies is tripled? (a) 3k ln (2) (b) 2k ln (3) (c) k ln (3) (d) 3k ln (3)


No Undo. Which of the following is/are irreversible process/es?

I. Free expansion of an ideal gas. II. A body sliding to rest because of friction. III. Two gases mixing in the same container. (a) I only (b) II only (c) III only (d) I, II and III


oTo Engine. An Otto engine compresses a mono-atomic gas to

1/15 of its volume during its cycle. What is the theoretical efficiency of the engine? (a) 0.661 (b) 0.836 (c) 0.977 (d) 0.989


Water Entropy. 1.5 kilograms of ice at 0

Compute its change in entropy. (a) 2.0 × 103 J/K (b) 2.0 × 105 J/K (c) 3.8 × 103 J/K (d) 3.8 × 105 J/K


o

C is

heated to 100

o

C.

EnTRUEpy. Which of the following statements regarding entropy

is/are TRUE? I. The change in entropy of a reversible cyclic process is zero. II. The entropy of an isolated system can never decrease. III. The entropy of a system in a reversible process is always increasing. (a) I only (b) II only (c) Both I and II (d) Both I and III


Reversible. Which of the following condition/s is/are necessary

for a reversible process to take place? I. Finite temperature drop in a heat flow II. Absence of heat exchange III. Thermal and mechanical equilibrium (a) I only (b) II only (c) II and III only (d) I, II, and III


Order vs Disorder. How is an ordered system compared with a

disordered system? (a) It has a higher number of microstates and has greater entropy. (b) It has a lower number of microstates and has greater entropy. (c) It has a higher number of microstates and has lesser entropy. (d) It has a lower number of microstates and has lesser entropy.


Microstates. The entropy of a system is increased by

(c > 0). If the system consists of N identical particles and initially has n microstates, what is the final number of microstates? (a)

ne −cS 0 /k

(b)

ne cS 0 /k

(c)

n(1

(d)

n(e cS 0 /k −

−

e cS 0 /k )−1

1)

1

−


cS 0

Answers

1. 2. 3. 4. 5. 6. 7. 8.

D D C A A A D D

9. D 10. B 11. C 12. C 13. C 14. D 15. B


Physics 73 Review

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