Heat Transfer PYQs Set 4 (PDF)

Set 4 of 7 · Questions 91-120 of 200

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Mere Teacher · Previous Year Questions NEET Physics · Heat Transfer · Set 4 (Q91-120)
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91. $A spherical black body with a radius of 12 cm radiates 440 W power at 500 K. If the radius were halved and the temperature doubled, the power radiated in watt would be$ (1) $225$ (2) $450$ (3) $900$ (4) $1800$ 92. $Certain substance emits only the wavelengths λ_{1}, λ_{2}, λ_{3} and λ_{4} when it is at a high temperature. When this substance is at a colder temperature, it will absorb only the following wavelengths$ (1) $λ_{1}$ (2) $λ_{2}$ (3) $λ_{1} and λ_{2}$ (4) $λ_{1}, λ_{2}, λ_{3} and λ_{4}$ 93. $The wavelength of maximum energy released during an atomic explosion was 2.93 \times 1 0^{- 10} m . Given that Wien's constant is 2.93 \times 1 0^{- 3} m -K, the maximum temperature attained must be of the order of$ (1) $1 0^{-7} K$ (2) $1 0^{7} K$ (3) $1 0^{-13} K$ (4) $5.86 \times 1 0^{7} K$ 94. $Newton’s law of cooling is a special case of$ (1) $Wien’s displacement law$ (2) $Kirchoff’s law$ (3) $Stefan’s law$ (4) $Planck’s law$ 95. $If black wire of platinum is heated, then its colour first appear red, then yellow and finally white. It can be understood on the basis of$ (1) $Wien's displacement law$ (2) $Prevost theroy of heat exchange$ (3) $Newton's law of cooling$ (4) $None of the above$ 96. $As compared to the person with white skin, the person with black skin will experience$ (1) $Less heat and more cold$ (2) $More heat and more cold$ (3) $More heat and less cold$ (4) $Less heat and less cold$ 97. $In a room where the temperature is 30 ℃, a body cools from 61 ℃ to 59 ℃ is 4 minutes. The time taken by the body to cool from 51 ℃ to 49 ℃ will be:$ (1) $4 minutes$ (2) $6 minutes$ (3) $5 minutes$ (4) $8 minutes$ 98. $The spectral energy distribution of star is maximum at twice temperature as that of sun. The total energy radiated by star is$ (1) $Twice as that of the sun$ (2) $Same as that of the sun$ (3) $Sixteen times as that of the sun$ (4) $One sixteenth of sun$ 99. $In MKS system, Stefan's constant is denoted by σ . In CGS system multiplying factor of σ will$ (1) $1$ (2) $1 0^{3}$ (3) $1 0^{5}$ (4) $1 0^{2}$ 100. $Which of the following statements is wrong$ (1) $Rough surfaces are better radiators than smooth surface$ (2) $Highly polished mirror like surfaces are very good radiators$ (3) $Black surfaces are better absorbers than white ones$ (4) $Black surfaces are better radiators than white$ 101. $A sphere at temperature 600K is placed in an environment of temperature is 200K. Its cooling rate is H. If its temperature reduced to 400K then cooling rate in same environment will become$ (1) $(3/16)H$ (2) $(16/3)H$ (3) $(9/27)H$ (4) $(1/16)H$ 102. $A black body radiates 20 W at temperature 22 7^{o} C . If temperature of the black body is changed to 72 7^{o} C then its radiating power will be$ (1) $120W$ (2) $240 W$ (3) $320 W$ (4) $360 W$ 103. $The temperature of a piece of iron is 2 7^{o} C and it is radiating energy at the rate of Q kW m^{- 2} . If its temperature is raised to 15 1^{o} C, the rate of radiation of energy will become approximately$ (1) $2 Q kW m^{- 2}$ (2) $4 Q kW m^{- 2}$ (3) $6 Q kW m^{- 2}$ (4) $8 Q kW m^{- 2}$ 104. $A black body at a temperature of 127°C radiates heat at the rate of 1 cal/ c m^{2} \times sec. At a temperature of 527°C the rate of heat radiation from the body in (cal/ c m^{2} \times sec) will be$ (1) $16.0$ (2) $10.45$ (3) $4.0$ (4) $2.0$ 105. $A liquid cools down from 70° C to 60°C in 5 min. The time taken to cool it from 60°C to 50°C will be$ (1) $5 min$ (2) $lesser than 5 min$ (3) $greater than 5 min$ (4) $lesser or greater than 5 min depending upon the density of the liquid$ 106. $The absolute temperatures of two black bodies are 2000 K and 3000 K respectively. The ratio of wavelengths corresponding to maximum emission of radiation by them will be$ (1) $2 : 3$ (2) $3 : 2$ (3) $9 : 4$ (4) $4 : 9$ 107. $A cylinder of radius R is surrounded by a cylindrical of inner radius R and outer radius 2R. The thermal conductivity of the material of the inner cylinder is K_{1} and that of the outer cylinder is K_{2} . Assuming no loss of heat, the effective thermal conductivity of the system for heart flowing along the length of the cylinder is:$ (1) $K_{1} + K_{2}$ (2) $\frac{2 K _{1} + 3 K _{2}}{2}$ (3) $\frac{K _{1} + K _{2}}{2}$ (4) $\frac{K _{1} + 3 K _{2}}{4}$ 108. $Which of the prism is used to see infra-red spectrum of light$ (1) $Rock-salt$ (2) $Nicol$ (3) $Flint$ (4) $Crown$ 109. $A black body radiates energy at the rate of EW / m^{2} at a high temperature TK . When the temperature is reduced to \frac{T}{2} K, the radiant energy will be$ (1) $\frac{E}{16}$ (2) $\frac{E}{4}$ (3) $4 E$ (4) $16 E$ 110. $Equal masses of two liquids are filled in two similar calorimeters. The rate of cooling will$ (1) $Depend on the nature of the liquids$ (2) $Depend on the specific heats of liquids$ (3) $Be same for both the liquids$ (4) $Depend on the mass of the liquids$ 111. $If the radius of a star is R and it acts as a black body, what would be the temperature of the star, in which the rate of energy production is Q$ (1) $Q /4πR2σ$ (2) $(Q /4πR2σ)-1/2$ (3) $(4πR2Q/σ)1/4$ (4) $(Q/ 4πR2σ)1/4$ 112. $Hot water kept in a beaker placed in a room cools from 7 0^{o} C to 60°C in 4 minutes. The time taken by it to cool from 6 9^{o} C to 5 9^{o} c will be$ (1) $The same 4 minutes$ (2) $More than 4 minutes$ (3) $Less than 4 minutes$ (4) $We cannot say definitely$ 113. $If a piece of metal is heated to temperature θ and then allowed to cool in a room which is at temperature θ_{0}, the graph between the temperature T of the metal and time t will be closest to:$ (1) (2) (3) (4) 114. $The temperatures of two bodies A and B are respectively 72 7^{o} C and 32 7^{o} C . The ratio H_{A} : H_{B} of the rates of heat radiated by them is$ (1) $727 : 327$ (2) $5 : 3$ (3) $25 : 9$ (4) $625 : 81$ 115. $Energy is being emitted from the surface of a black body at 127 ℃ temperature at the rate of 1.0\times106 J/sec- m2. Temperature of the black body at which the rate of energy emission is 16.0\times106 J/sec- m2 will be$ (1) $254 ℃$ (2) $508 ℃$ (3) $527 ℃$ (4) $727 ℃$ 116. $Two identical metal balls at temperature 20 0^{o} C and 40 0^{o} C kept in air at 2 7^{o} C . The ratio of net heat loss by these bodies is$ (1) $1/4$ (2) $½$ (3) $1/16$ (4) $\frac{47 3 ^{4} - 30 0 ^{4}}{67 3 ^{4} - 30 0 ^{4}}$ 117. $Two spheres made of same material have radii in the ratio 1: 2 Both are at same temperature. Ratio of heat radiation energy emitted per second by them is$ (1) $1 : 2$ (2) $1 : 8$ (3) $1 : 4$ (4) $1 : 16$ 118. $The amount of radiation emitted by a perfectly black body is proportional to$ (1) $Temperature on ideal gas scale$ (2) $Fourth root of temperature on ideal gas scale$ (3) $Fourth power of temperature on ideal gas scale$ (4) $Source of temperature on ideal gas scale$ 119. $A body cools from 6 0^{o} C to 5 0^{o} C in 10 minutes when kept in air at 3 0^{o} C . In the next 10 minutes its temperature will be$ (1) $Below 4 0^{o} C$ (2) $4 0^{o} C$ (3) $Above 4 0^{o} C$ (4) $Cannot be predicted$ 120. $A bucket full of hot water cools from 75 ℃ to 7 0^{0 C} in time T_{1}, from 70 ℃ to 65 ℃ in time T_{2} and from 65 ℃ to 60 ℃ in time T_{3}, then$ (1) $T_{1} = T_{2} = T_{3}$ (2) $T_{1} > T_{2} > T_{3}$ (3) $T_{1} < T_{2} < T_{3}$ (4) $T_{1} > T_{2} < T_{3}$