## THERMAL PROPERTIES OF MATTER QUIZ-8

JEE Advanced Physics Syllabus can be referred by the IIT aspirants to get a detailed list of all topics that are important in cracking the entrance examination. JEE Advanced syllabus for Physics has been designed in such a way that it offers very practical and application-based learning to further make it easier for students to understand every concept or topic by correlating it with day-to-day experiences. In comparison to the other two subjects, the syllabus of JEE Advanced for physics is developed in such a way so as to test the deep understanding and application of concepts.

Q71. Two tanks A and B contains water at 30°C and 80°C, respectively; calculate the amount of water that must be taken from each tank respectively to prepare 40 kg of water at 50°C:
•  24 kg, 16 kg
•  16 kg, 24 kg
•  20 kg, 20 kg
•  30 kg, 10 kg
Solution

72. Two metal strips that constitute a thermostat must necessarily differ in their
•  Mass
•  Length
•  Resistivity
•  Coefficient of linear expansion
Solution
72(d) Thermostat is used in electric apparatus like refrigerator, iron etc for automatic cut off. Therefore for metallic strips to bend on heating their coefficient if linear expansion should be different

Q73. A liquid takes 5 min to cool from 80°C to 50°C. How much time will it take to cool from 60°C to 30°C? The temperature of the surrounding is 20°C
•   5 min
•  9 min
•  4 min
•  12 min
Solution

Q74. Figure shows two air-filled bulbs connected by a U-tube partly filled with alcohol. What happens to the levels of alcohol in the limbs X and Y when an electric bulb placed midway between the bulbs is lighted?
•  The level of alcohol in limb X falls while that in limb Y rises
•  The level of alcohol in limb X rises which that in limb Y falls
•  The level of alcohol falls in both limbs
•  There is no change in the levels of alcohol in either of the two limbs
Solution
74(a) Black bulb absorbs more heat in comparison with painted bulb. So air in black bulb expands more. Hence the level of alcohol in limb X falls while that in limb Y rises

Q75. Two rods of length L_2 and coefficient of linear expansion Î±_2 are connected freely to a third rod of length L_1 of coefficient of linear expansion Î±_1to form an isosceles triangle. The arrangement is supported on the knife edge at the midpoint of L_1 which is horizontal. The apex of the isosceles tringle is to remain at a constant distance from the knife edge if
•  L_1/L_2 =Î±_2/Î±_1
•  L_1/L_2 =√(Î±_2/Î±_1 )
•  L_1/L_2 =2 Î±_2/Î±_1
•  L_1/L_2 =2√(Î±_2/Î±_1 )
Solution

Q76. A planet radiates heat at a rate proportional to the fourth power of its surface temperature T. If such a steady temperature of the planet is due to an exactly equal amount of heat received from the sun then which of the following statements is true?
•  The planet’s surface temperature varies inversely as the distance of the sun
•  The planet’s surface temperature varies directly as the square of its distance from the sun
• The planet’s surface temperature varies inversely as the square root of its distance from the sun
•  The planet’s surface temperature is proportional to the fourth power of distance from the sun
Solution
76.(c) Rate of loss of energy by unit area of the planet =ÏƒT^4, where Ïƒ is the Stefan’s constant. Let Q be the total energy emitted by the sun every second. If d is the distance of the planet from sun, then Q falls uniformly over the inner surface of the sphere of radius d. Rate of gain of heat by unit area of planet

Q77. Four spheres A,B,C and D have their radii in arithmetic progression and the specific heat capacities of their substances are in geometric progression. If the ratios of heat capacities of D and B to that of C and A are as 8:27. The ratio of masses of B and A is (assume same density for all spheres)
•  8:1
•  4:1
•  1:8
•  1:4
Solution

Q78. 10 g of ice at -20°C is dropped into a calorimeter containing 10 g of water at 10°C; the specific heat of water is twice that of ice. When equilibrium of redached, the calorimeter will contains
•  20 g of water
•  20 g of ice
•  10 g ice and 10 g of water
•  5 g ice and 15 g of water
Solution

Q79. A thin circular metal disc of radius 500.0 mm is set rotating about a central axis normal to its plane. Upon raising its temperature gradually, the radius increase to 507.5 mm. The percentage change in the rotational kinetic energy will be
•  1.5%
•  -1.5%
•  3%
•  >-3%
Solution

Q80. There are three thermometers-one in contact with the skin of the man, other in between the vest and the shirt and third in between the shirt and coat. The reading of the thermometers are 30°C,25°C and 22°C, respectively. If the vest and the shirt are of the same thickness, the ratio of their thermal conductivities is
•  9:25
•  25:9
•  5:3
• 3:5
Solution

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