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NCERT Solutions for class 11 Physics | Chapter 11 - Thermal Properties of Matter

(1) A person with dark skin as compared to a person with white skin will experience
[A] Less heat and less cold
[B] More heat and more cold
[C] More heat and less cold
[D] Less heat and more cold.
Answer: More heat and more cold
(2) The best ideal black body is
[A] Lamp of charcoal heated to high temperature
[B] Metal coated with a black dye
[C] Glass surface coated with coalter
[D] Hollow enclosure blackened inside and having a small hole
Answer: Hollow enclosure blackened inside and having a small hole

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(3) The process of heat transfer in which heat is transferred with actual migration of medium particles is known as (AFMC-94)
[A] Conduction
[B] Convection
[C] Radiation
[D] Reflection
Answer: Convection
(4) The flow of heat from a hot body to a cold body is an example of
[A] Isothermal process
[B] Reversible process
[C] Adiabatic process
[D] Irreversible process
Answer: Irreversible process
(5) A black body at hot temperature at 227°C radiates heat at a rate of 5 cal/cm²s. at a temperature of 727°C the rate of heat radiated per unit area will be
[A] 50 cal/cm²s
[B] 250 cal/cm²s
[C] 80 cal/cm²s
[D] 100 cal/cm²s
Answer: 80 cal/cm²s
(6) A bucket full of hot water is kept in a room and it cools from 75°C to 70°C in t1 minutes from 70°C to 65°C in t2 minutes and from 65°C to 60°C in t3 minutes; then
[A] t1 – t2 = t3
[B] t1 < t2 < t3
[C] t1 > t2 > t3
[D] t1 < t2 > t3
Answer: t1 < t2 < t3
(7) Two stars A and B radiate maximum energy at 3600°A and 3600°A respectively. Then the ratio of absolute temperatures of A and B is
[A] 256 : 81
[B] 81 : 256
[C] 3 : 4
[D] 4 : 3
Answer: 4 : 3
(8) A cup of tea cools from 80°C to 60°C in one minute. The ambient temperature is 30°C. in cooling from 60°C to 50°C, it will take.
[A] 50 sec
[B] 90 sec
[C] 60 sec
[D] 30 sec
Answer: 50 sec
(9) Unit of Stefans constant is given by
[A] W/ m K²
[B] W/ m² K²
[C] W²/ m² K4
[D] W/ mK
Answer: W/ m² K²
(10) The earth receives at its surface radiation from the sun at the rate of 1400 W/m². the distance of the centre of the sun from the surface of the earth is 1.5 1011 m and the radius of the sun is 7.0 108 m. treating sun as a black body, it follows from the above data that its surface temperature is,
[A] 5801 K
[B] 106 K
[C] 50.1 K
[D] 2801 C
Answer: 5801 K
(11) The temperature of a piece of metal is raised from 27°C to 51.2°C. the rate at which metal radiates energy increases nearly
[A] 1.36 times
[B] 2.36 times
[C] 3.36 times
[D] 4.36 times
Answer: 1.36 times
(12) The earth intercepts approximately one billionth of the power radiated by the sun. if the surface temperature of the sun were to drop by a factor of 2, the average radiant energy incident on earth per second would reduce by factor of
[A] 2
[B] 4
[C] 8
[D] 16
Answer: 16
(13) Emissivity of perfectly black body is
[A] 1
[B] 2
[C] 5
[D] 0
Answer: 1
(14) A body cools from 50°C to 46°C in 5 minutes and to 40°C in the next 10 minutes. The surrounding temperature is
[A] 30°C
[B] 28°C
[C] 36°C
[D] 32°C
Answer: 30°C
(15) Absorptive power of perfectly black body is
[A] Zero
[B] Infinity
[C] One
[D] Constant
Answer: One
(16) For which of the following process, the thermal conduction is maximum?
[A] Combustion
[B] Radiation
[C] Convection
[D] Conduction
Answer: Radiation
(17) A metal piece heated to T1°K. The temperature of the surrounding is T2°K. the heat in the surrounding due to radiation is proportional to
[A] (T14 – T24)
[B] (T1 – T2)4
[C] (T14 + T24)
[D] (T13 – T23)
Answer: (T14 – T24)
(18) A surface at temperature T0°K receives power P by radiation from a small sphere at temperature T >> T0 and at a distance d. if both T and d are doubled, the power received by surface will becomes approximately
[A] P
[B] 2p
[C] 4p
[D] 16p
Answer: 4p
(19) The good absorber of heat are
[A] Non-emitter
[B] Poor-emitter
[C] Good-emitter
[D] Highly polished
Answer: Good-emitter
(20) Co-efficient of reflection, coefficient of absorption and coefficient transmission are related as
[A] a + r + 1 = 1
[B] a + r + t1 1
[C] a + r = -t
[D] a1 r + 1
Answer: a + r + 1 = 1

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