Heat and Thermodynamics part-(2)

Total Questions: 44

11. Assertion (A): Large cold storage plants use ammonia as refrigerant while domestic refrigerators use chlorofluorocarbons. Reason (R) :Ammonia can be liquified at a ambient temperature at low pressure. [I.A.S. (PRE) 2000]

(a) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.

Correct Answer: (c) (A) is true, but (R) is false.

Solution:Assertion (A) is correct but reason (R) is false because ammonia can be qualified at the ambient temperature at high pressure not low pressure.

12. consider the following statement - [U.P.P.C.S.(pre) 2010]

Assertion (A): if ice collect in the freezer the cooling in the refrigerator is affected adversely.
Reason (R) : ice is a poor conductor.
select the correct answer using the codes given below.

(a) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.

Correct Answer: (a) Both (A) and (R) are true, and (R) is the correct explanation of (A).

Solution:Ice collects in the freezers is the result of vapour and moisture which is expelled by the food and ice tray .it adversely affects the cooling of the refrigerator, as ice is a poor conductor.

13. Consider the figure of a metal ball and a metal ring the given below : [I.A.S. (PRE) 1993]

the metal ball can just pass through the hole of a metal ring formed out for strip when the ball is heated it stuck but when the metal is heated -

(a) the ball can still pass through the ring as diameter expands on heating.
(b) the ball get suck because of the diameter of the hole decrease on expansion.
(c) the ball will still pass through the because the hole diameter does not change.
(d) the ball can still pass through because there is no change in the ring.

Correct Answer: (a) the ball can still pass through the ring as diameter expands on heating.

Solution:Most solids expand when heated and contract when cooled. The rate at which solids expand when heated depends on the substance. Metals tend to have higher rates of expansion than non-metal solids. When a metal ring is heated, there is an increase in outer diameter along with inner diameter. Thus, the ball can pass easily through it.

14. Strips of two metals A and B are firmly jointed together as shown in the figure. [I.A.S. (PRE) 1999]

Correct Answer: (b)

Solution:When two strips of different metals, say one of brass and the other of iron are welded or riveted together, the greater expansion of one metal results in the bending shown in option (b). Such a compound thin bar is called a bimetallic strip. When the strip is heated one side of the double strip bent into a curve.

15. Assertion (A): A piece of copper and a piece of glass are heated to the same temperature. When touched, thereafter, the copper piece appears hotter than the glass piece. [I.A.S. (PRE) 2001]

Reason (R): The density of copper is more than that of glass.

(a) both (A) and (R) are true and (R) is the correct explanation of (A).
(b) (b) Both (A) and (R)are true but (R) is not a correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.

Correct Answer: (b) (b) Both (A) and (R)are true but (R) is not a correct explanation of (A).

Solution:Copper is a very good conductor of heat. So it allows the maximum amount of heat to pass through it from one point to other. But glass is a poor conductor of heat and hence it allows a very little amount of heat to pass through it.

The density of copper is 8920-8960 kg/m³ and the density of glass is equal to 2400-2800 kg/m³. Thus the density of copper is more than that of glass, but it is not the correct reason of the given assertion. Hence the correct answer is option (b).

16. In winter you touch a log of wood and a rod of iron. you will feel rod of iron is colder because- [41st B.P.S.C. (Pre) 1996]

(a) The heat of rod of iron is less than the heat of log of wood.
(b) In comparison to wood, iron is good conductor of heat.
(c) In comparison to wood, iron is bad conductor of heat .
(d) The rod of iron is heavier than the log of wood.

Correct Answer: (a) The heat of rod of iron is less than the heat of log of wood.

Solution:In winter, if we touch a log of wood and a rod of iron, we feel that rod of iron is cold. It is because of the fact that in comparison to wood, iron is a good conductor of heat.

When both the metal and the wood are at the same temperature, heat will flow from iron. Similarly, when we touch wood, a poor conductor, heat does not flow from it. Hence iron rod will feel colder as compared to wood.

17. If the temperature of air increases, how would it affect its ability to assume water vapour- [Jharkhand P.C.S. (Pre) 2003]

(a) Decrease.
(b) Increase.
(c) Firstly decrease, then again increase.
(d) Remains constant.

Correct Answer: (b) Increase.

Solution:There is a direct relation between the atmospheric humidity and temperature. The ability of air to assume water vapour depends on its temperature. Thus, if temperature of air is increased then automatically its ability to hold water vapour will also be increased.

18. In the night of strong wind, dew is not formed because: [40th B.P.S.C. (PRE) 1995]

(a) Rate of evaporation is fast.
(b) Moisture in air is low.
(c) temperature is high.
(d) sky is not clear.

Correct Answer: (a) Rate of evaporation is fast.

Solution:Dew is not formed in the night of strong wind as due to strong wind the rate of evaporation is fast.Thus the particle of the dew tend to evaporate.

19. Which of the following statement is not true ? [U.P.P.C.S.(pre) 2007]

(a) air conditioner and air cooler both maintain the temperature.
(b) air conditioner and air cooler both maintain the humidity.
(c) air conditioner maintain humidity but the air cooler does not maintain the humidity.
(d) both control motion of air.

Correct Answer: (b) air conditioner and air cooler both maintain the humidity.

Solution:Air conditioner and air cooler both maintain temperature and the motion of air but the air conditioner have the ability to maintain the humidity while the air cooler does not have the ability to maintain humidity thus it is clear that option (b) is not true.

20. What does the air conditioner installed in a room control ? [U.P.P.C.S.(MAINS) 2011]

(a) temperature only.
(b) humidity and temperature only.
(c) pressure and temperature only.
(d) humidity pressure and temperature.

Correct Answer: (b) humidity and temperature only.

Solution:

Temperature: Air conditioners are designed to lower the temperature of the air in a room.
Humidity: Air conditioners remove moisture from the air, thereby reducing humidity.
Pressure: Air conditioners do not significantly alter the air pressure within a room. The pressure inside a room is usually very close to the outside atmospheric pressure.

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Heat and Thermodynamics part-(2)