Heat Transfer PYQs Set 2 (PDF)

Set 2 of 7 · Questions 31-60 of 200

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Mere Teacher · Previous Year Questions NEET Physics · Heat Transfer · Set 2 (Q31-60)
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31. $Liquid is filled in a vessel which is kept in a room with temperature 2 0^{o} C . When the temperature of the liquid is 8 0^{o} C, then it loses heat at the rate of 60 cal / sec . What will be the rate of loss of heat when the temperature of the liquid is 4 0^{o} C$ (1) $180 cal / sec$ (2) $40 cal / sec$ (3) $30 cal / sec$ (4) $20 cal / sec$ 32. $A body radiates energy 5W at a temperature of 127 ℃ . If the temperature is increased to 927 ℃, then it radiates energy at the rate of$ (1) $410W$ (2) $81W$ (3) $405W$ (4) $200 W$ 33. $Two identical bodies are made of a material for which the heat capacity increases with temperature. One of these is at 100ºC, while the other one is at 0ºC. If the two bodies are brought into contact, then assuming no heat loss, the final common temperature is$ (1) $0º C$ (2) $50º C$ (3) $more then 50º C$ (4) $less than 50º C but greater than 0º C$ 34. $Suppose the sun expands so that its radius becomes 100 times its present radius and its surface temperature becomes half of its present value. The total energy emitted by it then will increase by a factor of$ (1) $1 0^{4}$ (2) $625$ (3) $256$ (4) $16$ 35. $A hot body will radiate heat most rapidly if its surface is$ (1) $White & polished$ (2) $White & rough$ (3) $Black & polished$ (4) $Black & rough$ 36. $A particular star (assuming it as a black body) has a surface temperature of about 5 \times 1 0^{4} K . The wavelength in nanometers at which its radiation becomes maximum is (b = 0.0029 mK)$ (1) $48$ (2) $58$ (3) $60$ (4) $70$ 37. $The energy emitted per second by a black body at 2 7^{o} C is 10 J . If the temperature of the black body is increased to 32 7^{o} C, the energy emitted per second will be$ (1) $20 J$ (2) $40 J$ (3) $80 J$ (4) $160 J$ 38. $A cup of tea cools from 80°C to 60°C in one minute. The ambient temperature is 30°C. In cooling from 60°C to 50°C it will take-$ (1) $30 seconds$ (2) $60 seconds$ (3) $96 seconds$ (4) $48 seconds$ 39. $Which of the following is the correct device for the detection of thermal radiation$ (1) $Constant volume thermometer$ (2) $Liquid-in-glass thermometer$ (3) $Six's maximum and minimum thermometer$ (4) $Thermopile$ 40. $The temperature of sun is 5500 K and it emits maximum intensity radiation in the yellow region (5.5 \times 1 0^{- 7} m) . The maximum radiation from a furnace occurs at wavelength 11 \times 1 0^{- 7} m . The temperature of furnace is$ (1) $1125 K$ (2) $2750 K$ (3) $5500 K$ (4) $11000 K$ 41. $The wavelength of maximum emitted energy of a body at 700 K is 4.08 μm . If the temperature of the body is raised to 1400 K, the wavelength of maximum emitted energy will be$ (1) $1.02 μm$ (2) $16.32 μm$ (3) $8.16 μm$ (4) $2.04 μm$ 42. $A black body is at a temperature 300 K. It emits energy at a rate, which is proportional to$ (1) $300$ (2) $(300)^{2}$ (3) $(300)^{3}$ (4) $(300)^{4}$ 43. $A black body radiates energy at the rate of 1 \times 1 0^{5} J / s \times m^{2} at temperature of 22 7^{o} C. The temperature to which it must be heated so that it radiates energy at rate of 1 \times 1 0^{9} J/ s m^{2}, is$ (1) $5000 K$ (2) $5000 ℃$ (3) $500 K$ (4) $500 ℃$ 44. $A piece of blue glass heated to a high temperature and a piece of red glass at room temperature, are taken inside a dimly lit room then$ (1) $The blue piece will look blue and red will look as usual$ (2) $Red look brighter red and blue look ordinary blue$ (3) $Blue shines like brighter red compared to the red piece$ (4) $Both the pieces will look equally red.$ 45. $If the temperature of the sun becomes twice its present temperature, then$ (1) $Radiated energy would be predominantly in infrared$ (2) $Radiated energy would be predominantly in ultraviolet$ (3) $Radiated energy would be predominantly in X-ray region$ (4) $Radiated energy would become twice the present radiated energy$ 46. $The maximum wavelength of radiation emitted at 2000 K is 4μm. What will be the maximum wavelength of radiation emitted at 2400 K?$ (1) $3.33 μm$ (2) $0.66 μm$ (3) $1 μm$ (4) $1 m$ 47. $The original temperature of a black body is 72 7^{o} C . The temperature at which this black body must be raised so as to double the total radiant energy, is$ (1) $971 K$ (2) $1190 K$ (3) $2001 K$ (4) $1458 K$ 48. $The temperature at which a black body of unit area loses its energy at the rate of 1 joule/second is$ (1) $- 6 5^{o} C$ (2) $6 5^{o} C$ (3) $65 K$ (4) $None of these$ 49. $A thin square steel plate with each side equal to 10 cm is heated by a blacksmith. The rate of radiated energy by the heated plate is 1134 W. The temperature of the hot steel plate is (Stefan's constant σ = 5.67 \times 1 0^{- 8} watt m^{- 2} K^{- 4}, emissivity of the plate = 1)$ (1) $1000 K$ (2) $1189 K$ (3) $2000 K$ (4) $2378 K$ 50. $The wavelength of maximum energy released during an atomic explosion was 2.93 \times 1 0^{- 10} m . Given that Wein's constant is 2.93 \times 1 0^{- 3} m - K, the maximum temperature attained must be of the order of$ (1) $1 0^{- 7} K$ (2) $1 0^{7} K$ (3) $1 0^{- 13} K$ (4) $5.86 \times 1 0^{7} K$ 51. $At temperature T, the power radiated by a body is Q watts. At the temperature 3T the power radiated by it will be$ (1) $3 Q$ (2) $9 Q$ (3) $27 Q$ (4) $81 Q$ 52. $Two spheres P and Q, of same colour having radii 8 cm and 2 cm are maintained at temperatures 12 7^{o} C and 52 7^{o} C respectively. The ratio of energy radiated by P and Q is$ (1) $0.054$ (2) $0.0034$ (3) $1$ (4) $2$ 53. $The energy supply being cut-off, an electric heater element cools down to the temperature of its surroundings, but it will not cool further because$ (1) $Supply is cut off$ (2) $It is made of metal$ (3) $Surroundings are radiating$ (4) $Element & surroundings have same temp.$ 54. $Rate of cooling at 600K, if surrounding temperature is 300K is R. The rate of cooling at 900K is$ (1) $\frac{16}{3} R$ (2) $2 R$ (3) $3 R$ (4) $\frac{2}{3} R$ 55. $On investigation of light from three different stars A, B and C, it was found that in the spectrum of A the intensity of red colour is maximum, in B the intensity of blue colour is maximum and in C the intensity of yellow colour is maximum. From these observations it can be concluded that$ (1) $The temperature of A is maximum, B is minimum and C is intermediate$ (2) $The temperature of A is maximum, C is minimum and B is intermediate$ (3) $The temperature of B is maximum, A is minimum and C is intermediate$ (4) $The temperature of C is maximum, B is minimum and A is intermediate$ 56. $The power radiated by a black body in P and it radiated maximum energy at wavelength, λ_{0} . If the temperature of the black body is now changes so that it radiates maximum energy at wavelength \frac{3}{4} λ_{0}, the power radiated by it becomes nP. The value of n is:$ (1) $\frac{3}{4}$ (2) $\frac{81}{256}$ (3) $\frac{256}{81}$ (4) $\frac{4}{3}$ 57. $Half part of ice block is covered with black cloth and rest half is covered with white cloth and then it is kept in sunlight. After some time clothes are removed to see the melted ice. Which of the following statements is correct$ (1) $Ice covered with white cloth will melt more$ (2) $Ice covered with black cloth will melt more$ (3) $Equal ice will melt under both clothes$ (4) $It will depend on the temperature of surroundings of ice$ 58. $The intensity of radiation emitted by the sun has its maximum value at a wavelength of 510 nm and that emitted by the north star has the maximum value at 350 nm . If these stars behave like black bodies, then the ratio of the surface temperature of the sun and north star is$ (1) $1.46$ (2) $0.69$ (3) $1.21$ (4) $0.83$ 59. $Two black metallic spheres of radius 4m, at 2000 K and 1m at 4000 K will have ratio of energy radiation as$ (1) $1 : 1$ (2) $4 : 1$ (3) $1 : 4$ (4) $2 : 1$ 60. $When p calories of heat is given to a body, it absorbs q calories; then the absorbtion power of body will be$ (1) $p / q$ (2) $q / p$ (3) $p^{2} / q^{2}$ (4) $q^{2} / p^{2}$