Heat Transfer PYQs Set 5 (PDF)

Set 5 of 7 · Questions 121-150 of 209

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Mere Teacher · Previous Year Questions JEE Main Physics · Heat Transfer · Set 5 (Q121-150)
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121. $The amount of radiation emitted by a perfectly black body is proportional to$ (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) $Source of temperature on ideal gas scale$ 122. $A body cools from 6 0^{o} C to 5 0^{o} C in 10 minutes when kept in air at 3 0^{o} C . In the next 10 minutes its temperature will be$ (1) $Below 4 0^{o} C$ (2) $4 0^{o} C$ (3) $Above 4 0^{o} C$ (4) $Cannot be predicted$ 123. $A bucket full of hot water cools from 75 ℃ to 7 0^{0 C} in time T_{1}, from 70 ℃ to 65 ℃ in time T_{2} and from 65 ℃ to 60 ℃ in time T_{3}, then$ (1) $T_{1} = T_{2} = T_{3}$ (2) $T_{1} > T_{2} > T_{3}$ (3) $T_{1} < T_{2} < T_{3}$ (4) $T_{1} > T_{2} < T_{3}$ 124. $Two spheres of radii in the ratio 1 : 2 and densities in the ratio 2 : 1 and of same specific heat, are heated to same temperature and left in the same surrounding. Their rate of cooling will be in the ratio:$ (1) $2 : 1$ (2) $1 : 1$ (3) $1 : 2$ (4) $1 : 4$ 125. $If the temperature of the sun were to be increased from T to 2T and its radius from R to 2R, then the ratio of the radiant energy received on the earth to what it was previously will be$ (1) $4$ (2) $16$ (3) $32$ (4) $64$ 126. $The rates of cooling of two different liquids put in exactly similar calorimeters and kept in identical surroundings are the same if$ (1) $The masses of the liquids are equal$ (2) $Equal masses of the liquids at the same temperature are taken$ (3) $Different volumes of the liquids at the same temperature are taken$ (4) $Equal volumes of the liquids at the same temperature are taken$ 127. $If wavelengths of maximum intensity of radiations emitted by the sun and the moon are 0.5 \times 1 0^{- 6} m and 1 0^{- 4} m respectively, the ratio of their temperatures is$ (1) $1/100$ (2) $1/200$ (3) $100$ (4) $200$ 128. $The maximum wavelength of radiations emitted at 900 K is 4 μm . What will be the maximum wavelength of radiations emitted at 1200 K$ (1) $3 μm$ (2) $0.3 μm$ (3) $1 μm$ (4) $1 m$ 129. $Star A has radius r surface temperature T while star B has radius 4r and surface temperature T/2. The ratio of the power of two starts, P_{A} : P_{B} is$ (1) $16 : 1$ (2) $1 : 16$ (3) $1 : 1$ (4) $1 : 4$ 130. $The radiant energy from the sun incident normally at the surface of earth is 20 kcal/ m^{2} min. What would have been the radiant energy incident normally on the earth, if the sun had a temperature twice of the present one$ (1) $160 kcal/ m^{2} min$ (2) $40 kcal/ m^{2} min$ (3) $320 kcal/ m^{2} min$ (4) $80 kcal/ m^{2} min$ 131. $A body takes T minutes to cool from 6 2^{0} C to 6 1^{0} C when the surrounding temperature is 3 0^{0} C. The time taken by the body to cool from 4 6^{0} C to 45. 5^{0} C is$ (1) $Greater than T minutes$ (2) $Equal to T minutes$ (3) $Less than T minutes$ (4) $Equal to T/2 minutes$ 132. $A cup of tea cools from 80 ℃ to 60 ℃ in one minute. The ambient temperature is 30 ℃ . In cooling from 60 ℃ to 50 ℃ it will take$ (1) $30 seconds$ (2) $60 seconds$ (3) $90 seconds$ (4) $48 seconds$ 133. $The ratio of energy of emitted radiation of a black body at 27 ℃ and 927 ℃ is$ (1) $1 : 4$ (2) $1 : 16$ (3) $1 : 64$ (4) $1 : 256$ 134. $The rectangular surface of area 8 cm \times 4cm of a black body at a temperature of 12 7^{o} C emits energy at the rate of E per second. If the length and breadth of the surface are each reduced to half of the initial value and the temperature is raised to 32 7^{o} C, the rate of emission of energy will become$ (1) $\frac{3}{8} E$ (2) $\frac{81}{16} E$ (3) $\frac{9}{16} E$ (4) $\frac{81}{64} E$ 135. $A body takes 4 minutes to cool from 100^{\circ} C to 70^{\circ} c . If temperature of the surrounding is 20^{\circ} C . The time taken by it to cool from 70^{\circ} C to 50^{\circ} C is$ (1) $13/3 min$ (2) $13 min$ (3) $3 min$ (4) $6 min$ 136. $Coefficient of linear expansion of brass and steel rods are α_{1} and α_{2} . Lengths of brass and steel rods are l_{1} and l_{2} respectively. If (l_{2} - l_{1}) is maintained same at all temperatures, which one of the following relations holds good?$ (1) $α_{1} l_{1} = α_{2} l_{2}$ (2) $α_{1} l_{2} = α_{2} l_{1}$ (3) $α_{1} l_{2}^{2} = α_{2} l_{1}^{2}$ (4) $α_{1}^{2} l_{2} = α_{2}^{2} l_{1}$ 137. $A black body at a temperature of 227 ℃ radiates heat energy at the rate of 5 cal/cm2-sec. At a temperature of 727 ℃, the rate of heat radiated per unit area in cal/cm2 will be$ (1) $80$ (2) $160$ (3) $250$ (4) $500$ 138. $Two metallic spheres S_{1} and S_{2} are made of the same material and have identical surface finish. The mass of S_{1} is three times that of S_{2} . Both the spheres are heated to the same high temperature and placed in the same room having lower temperature but are thermally insulated from each other. The ratio of the initial rate of cooling of S_{1} to that of S_{2} is$ (1) $1/ 3$ (2) $(1/3)^{1/3}$ (3) $1/ 3$ (4) $3 /1$ 139. $The area of a hole of heat furnace is 1 0^{- 4} m^{2} . It radiates 1.58 \times 1 0^{5} calories of heat per hour. If the emissivity of the furnace is 0.80, then its temperature is$ (1) $1500 K$ (2) $2000 K$ (3) $2500 K$ (4) $3000 K$ 140. $We consider the radiation emitted by the human body. Which of the following statements is true$ (1) $The radiation is emitted only during the day$ (2) $The radiation is emitted during the summers and absorbed during the winters$ (3) $The radiation emitted lies in the ultraviolet region and hence is not visible$ (4) $The radiation emitted is in the infra-red region$ 141. $A black body radiates at the rate of W watts at a temperature T. If the temperature of the body is reduced to T/3, it will radiate at the rate of (in Watts)$ (1) $\frac{W}{81}$ (2) $\frac{W}{27}$ (3) $\frac{W}{9}$ (4) $\frac{W}{3}$ 142. $The formation of ice is started in a lake with water at 0°C. When the atmospheric temperature is -10°C. If time taken for 1 cm of ice to be formed is 7 hours, the time taken for the thickness of ice to increase from 1cm to 2 cm is:$ (1) $less than 7 hours$ (2) $7 hours$ (3) $more than 14 hours$ (4) $more than 7 hours but less than 14 hours$ 143. $The temperatures of two bodies A and B are 72 7^{o} C and 12 7^{o} C . The ratio of rate of emission of radiations will be$ (1) $727/127$ (2) $625/16$ (3) $1000/400$ (4) $100/16$ 144. $In Newton's experiment of cooling, the water equivalent of two similar calorimeters is 10 gm each. They are filled with 350 gm of water and 300 gm of a liquid (equal volumes) separately. The time taken by water and liquid to cool from 7 0^{o} C to 6 0^{o} C is 3 min and 95 sec respectively. The specific heat of the liquid will be$ (1) $0.3 Cal/gm \times°C$ (2) $0.5 Cal/gm \times°C$ (3) $0.6 Cal/gm \times°C$ (4) $0.8 Cal/gm \times°C$ 145. $If between wavelength λ and λ + dλ, e_{λ} and a_{λ} be the emissive and absorptive powers of a body and E_{λ} be the emissive power of a perfectly black body, then according to Kirchoff's law, which is true$ (1) $e_{λ} = a_{λ} = E_{λ}$ (2) $e_{λ} E_{λ} = a_{λ}$ (3) $e_{λ} = a_{λ} E_{λ}$ (4) $e_{λ} a_{λ} E_{λ} = constant$ 146. $A black body has maximum wavelength λ_{m} at temperature 2000 K . Its corresponding wavelength at temperature 3000 K will be$ (1) $\frac{3}{2} λ_{m}$ (2) $\frac{2}{3} λ_{m}$ (3) $\frac{4}{9} λ_{m}$ (4) $\frac{9}{4} λ_{m}$ 147. $A body cools from 6 0^{o} C to 5 0^{o} C in 10 minutes. If the room temperature is 2 5^{o} C and assuming Newton's law of cooling to hold good, the temperature of the body at the end of the next 10 minutes will be$ (1) $38. 5^{o} C$ (2) $4 0^{o} C$ (3) $42.8 5^{o} C$ (4) $4 5^{o} C$ 148. $The ratio of radiant energies radiated per unit surface area by two bodies is 16 : 1, the temperature of hotter body is 1000K, then the temperature of colder body will be$ (1) $250 K$ (2) $500 K$ (3) $1000 K$ (4) $62.5 K$ 149. $The rectangular surface of area 8 cm \times 4 cm of a black body at a temperature of 127 ℃ emits energy at the rate of E per second. If the length and breadth of the surface are each reduced to half of the initial value and the temperature is raised to 327 ℃, the rate of emission of energy will become$ (1) $\frac{3}{8} E$ (2) $\frac{81}{16} E$ (3) $\frac{9}{16} E$ (4) $\frac{81}{64} E$ 150. $If the temperature of a hot body is increased by 50% then the increase in the quantity of emitted heat radiation will be$ (1) $125%$ (2) $200%$ (3) $300%$ (4) $400%$