Heat and Thermodynamics part-(2)

Total Questions: 44

31. An assertion and its reason is given below: [U.P.R.O/A.R.O.(pre) 2016]

Assertion (A) : Light coloured cloths are preferred in summer.
Reason (R) : light colour are poor absorber of heat.
which one among these is the right answer.

(a) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true, and (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:White and light coloured cloths are poor absorbers of heat that is why such clothes are preferred in summer.So both the (A) and (R) correctly explains (A).

32. loss of water from the body through perspiration depends on : [U.P.B.E.O. (PRE) 2019]

(a) atmospheric humidity only.
(b) atmospheric temperature only.
(c) both (a) and (b).
(d) none of (a) and (b).

Correct Answer: (c) both (a) and (b).

Solution:loss of water from the body through perspiration depends on both atmospheric temperature and atmospheric humidity. Perspiration or sweating allows the body to regulate its temperature. The rate of sweating depends on many factors and is increased in proportion to the work rate and the environmental temperature and humidity.

33. The most important function of the perspiration is to : [R.A.S./R.T.S (PRE) 1994-95]

(a) regulate body temperature.
(b) regulate body water supply.
(c) get rid of body poison.
(d) keep the skin pores clear to dirt.

Correct Answer: (a) regulate body temperature.

Solution:Perspiration is often related to heat when there is a rise in the temperature of the surrounding the body heats up and that be dangerous. The problem will occur with the running of organs and even heat strokes can arise which leads to heart attack to death.

It is perspiration that cools the body down. The sweat released onto the body cools it down and when the watery substance evaporates from the skin it takes the heat with it giving a cooling effect.

34. A fan produce feeling of comfort during the hot weather because - [M.P.P.C.S.(PRE) 2008, 67th B.P.S.C. (PRE) 2022]

(a) fans supplies cold air.
(b) our perspiration evaporate rapidly.
(c) our body radiate more heat.
(d) conductivity of air increase.

Correct Answer: (b) our perspiration evaporate rapidly.

Solution:In summer a ceiling fan in the counterclockwise direction can help to cool our home by pushing cool air down . During the hot summer months though this wind chill effect can work to your advantage by providing a breeze that can help evaporate the skin moisturise quickly creating a cool feeling.

35. In an earthen pitcher, the water remains cold due to the process of: [U.P.P.C.S.(Pre) 2012]

(a) Condensation.
(b) Evaporation.
(c) Sublimation.
(d) None of the above.

Correct Answer: (b) Evaporation.

Solution:In an earthen pitcher, water remains cold due to the process of evaporation. The water seeps through the small pores of the pitcher, evaporates from the surface, and in doing so, absorbs heat from the surrounding water, thus cooling it down.

36. On a specific day and time, the temperature was 48°C Churu and 24°C Shimla. Two metallic cups identical in all respects contained water at 95°C in Churu and 71°C in Shimla. Which one of these two cups reached room temperature first? [R.A.S/R.T.S.(Pre) 2008]

(a) Cup in Churu.
(b) Cup in Shimla.
(c) Both cups reached room temperature at the same time.
(d) Data are not enough to find out result.

Correct Answer: (c) Both cups reached room temperature at the same time.

Solution:

The rate of heat loss of an object is called cooling rate.
Rate of heat loss (ΔQ)∝ Temperature difference (ΔT)
: 95 ° - 48 ° = 47 ° and 71 ° - 24 ° = 47 °
Because of the temperature difference (ΔT) is similar in both Thus, both cups reach the room temperature at the same time.

37. A hot body cools from 90°C to 75°C in 25 seconds The same body in further cooling from 75°C to 60°C will take how much time? [U.P. P.C.S. (Mains) 2017]

(a) 25 seconds.
(b ) Less than 25 seconds.
(c) More than 25 seconds.
(d) Nothing can be said.

Correct Answer: (c) More than 25 seconds.

Solution:Newton's law of cooling states that the rate of loss of heat by a body is directly proportional to the temperature difference between the body and its surroundings.
As the temperature difference between the body and its surroundings will be lesser in the second case, so the time taken in cooling from 75°C to 60°C will be more than 25 seconds.

38. Consider the following statements regarding 'heat wave' : [69th B.P.S.C. (Pre) 2023]

1. Heat wave is considered if the maximum temperature of a station reaches at least 30°C or more for plains.
2. Heat wave is considered if the maximum temperature of a station reaches at least 40°C or more for hilly regions.
Which of the above statements is/are correct?

(a) Both 1 and 2
(b) Only 1
(c) Only 2
(d) Neither 1 nor 2

Correct Answer: (d) Neither 1 nor 2

Solution:Heat wave is considered when temperature of a station reaches at least 40°C or more in plains and at least 30°C of more in hilly regions. Hence, both statements are incorrect.

39. In the season of summer we experience a humid heat when weather: [U.P.P.C.S.(pre) 2003]

(a) Start of summer.
(b) Middle of summer.
(c) Scorching weather.
(d) humid weather.

Correct Answer: (d) humid weather.

Solution:In the season of summer when the weather is humid we experience humid heat.

40. Xeric condition refers to - [U.P.R.O/A.R.O. (Pre) 2014]

(a) low temperature.
(b) low humidity.
(c) high evaporation.
(d) extreme temperature.

Correct Answer: (b) low humidity.

Solution:Xeric condition refers to low humidity. Xeric condition is characterized by an inadequate supply of water. These conditions exist in arid habitats, extremely cold habitats, and in salt marshes.

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Heat and Thermodynamics part-(2)