2. The sun shines on a 150 m2 road surface so it is at 45°C. Below the 5cm thick asphalt(average conductivity of 0.06 W/m K), is a layer of rubbles at 15°C. Find the rate of
Correct : B. 5400 w
3. A water-heater is covered with insulation boards over a total surface area of 3 m2. The inside board surface is at 75°C and the outside being at 20°C and the conductivity of material being 0.08 W/m K. Find the thickness of board to limit the heat transfer loss to 200 W ?
Correct : D. 0.066 m
4. A large heat exchanger transfers a total of 100 MW. Assume the wall separating steam and seawater is 4 mm of steel, conductivity 15 W/m K and that a maximum of 5°C difference between the two fluids is allowed. Find the required minimum area for the heat transfer.
Correct : D. 480 m2
5. The black grille on the back of a refrigerator has a surface temperature of 35°C with a surface area of 1 m2. Heat transfer to the room air at 20°C takes place with convective heat transfer coefficient of 15 W/Km^2. How much energy is removed during 15 minutes of operation?
Correct : A. 202.5 kj
6. A small light bulb (25 W) inside a refrigerator is kept on and 50 W of energy from the outside seeps into the refrigerated space. How much of temperature difference to the ambient(at 20°C) must the refrigerator have in its heat exchanger having an area of 1 m2 and heat transfer coefficient of 15 W/Km2 to reject the leak of energy.
Correct : B. 5°c
7. As the car slows down, the brake shoe and steel drum continuously absorbs 25 W. Assume a total outside surface area of 0.1 m2 with a convective heat transfer coefficient of 10 W/Km2 to the air at 20°C. How hot does the outside brake and drum surface become when steady conditions are reached?
Correct : C. 45°c
8. A burning wood in the fireplace has a surface temperature of 450°C. Assume the emissivity to be 1 and find the radiant emission of energy per unit area.
Correct : A. 15.5 kw/m2
9. 5 cm in diameter, through which 400 W of electric energy is deposited. Assume the surface emissivity to be 0.9 and neglecting incoming radiation, find the rod surface temperature?
Correct : D. 1000k
10. A water-heater is covered up with insulation boards over a total surface area of 3 m2. The inside board surface is at 75°C and the outside surface is at 20°C and the board material has a conductivity of 0.08 W/m K. How thick a board should it be to limit the heat transfer loss to 200 W ?
Correct : A. 0.066 m
11. 16 W/m K, with a temperature difference between the two sides of 20°C.
Correct : B. 213 w/m2
12. A 2 m2 window has a surface temperature of 15°C and the outside wind is blowing air at 2°C across it with a convection heat transfer coefficient of h = 125 W/m2K. What is the total heat transfer loss?
Correct : D. 3250 w
13. A radiant heating lamp has a surface temperature of 1000 K with ε = 0.8. How large a surface area is needed to provide 250 W of radiation heat transfer?
16. The transient response of a solid can be determined by the equation. (Where, P is density, V is volume, c is specific heat and A is area)
Correct : D. – p v c = h a (t – t0)
17. Transient condition means
Correct : A. conduction when temperature at a point varies with time
18. Which of the following is not correct in a transient flow process?
Correct : C. there is no accumulation of energy inside the control volume
19. The curve for unsteady state cooling or heating of bodies is
Correct : D. exponential curve asymptotic to time axis
20. What is the wavelength band for TV rays?
Correct : B. 1 * 10 3 to 2 * 10 10 micron meter
21. Thermal conductivity is defined as the heat flow per unit time
Correct : D. across unit area where the temperature gradient is unity
22. Mark the matter with least value of thermal conductivity
Correct : A. air
23. Which one of the following forms of water have the highest value of thermal conductivity?
Correct : C. solid ice
24. The average thermal conductivities of water and air conform to the ratio
Correct : B. 25:1
25. Identify the very good insulator
Correct : D. glass wool
26. Most metals are good conductor of heat because of
Correct : B. free electrons and frequent collision of atoms
27. Heat conduction in gases is due to
Correct : A. elastic impact of molecules
28. The heat energy propagation due to conduction heat transfer will be minimum for
Correct : C. air
29. Cork is a good insulator because
Correct : D. it is porous
30. Choose the false statement
Correct : B. thermal conductivity decreases with increase in the density of the substance
31. A composite wall generally consists of
Correct : B. multiple heterogeneous layers
32. Three metal walls of the same thickness and cross sectional area have thermal conductivities k, 2k and 3k respectively. The temperature drop across the walls (for same heat transfer) will be in the ratio
Correct : A. 3:2:1
33. A composite wall is made of two layers of thickness δ1 and δ2 having thermal conductivities k and 2k and equal surface area normal to the direction of heat flow. The outer surface of composite wall are at 100 degree Celsius and 200 degree Celsius. The minimum surface temperature at the junction is 150 degree Celsius. What will be the ratio of wall thickness?
Correct : C. 1:2
34. A pipe carrying steam at 215.75 degree Celsius enters a room and some heat is gained by surrounding at 27.95 degree Celsius. The major effect of heat loss to surroundings will be due to
Correct : C. radiation
35. “Radiation cannot be affected through vacuum or space devoid of any matter”. True or false
Correct : B. false
36. A composite wall of a furnace has two layers of equal thickness having thermal conductivities in the ratio 2:3. What is the ratio of the temperature drop across the two layers?
Correct : B. 3:2
37. According to Indian Standards, it is recommended that the overall thermal transmittance of a roof should not be more than kcal/m2 h deg C.
Correct : A. 2.00
38. The process of direct transmission of heat through a material is known as
Correct : A. conduction
39. Thermal insulation keeps the room cool in winters and hot in summers.
Correct : B. false
40. The amount of heat flow through a unit area of material of unit thickness in one hour, when the temperature difference is maintained at 1°C is known as of the material.
Correct : A. thermal conductivity
41. The reciprocal of thermal conductivity is known as
Correct : D. thermal resistivity
42. Which of the following is the correct relationship between thermal resistance and thermal conductivity?
Correct : C. r = l/k
43. Surface resistance is the reciprocal of
Correct : A. surface coefficient
44. Thermal damping is given by the equation D = (T-t/T) x 100. Here, T denotes
Correct : A. outside temperature range
45. Which of the following is the correct relation between thermal transmittance and thermal time constant?
Correct : C. t = q/u
46. Which of the following is not a quality of a good thermal insulating material?
Correct : B. it should have a low thermal resistance
47. Reflective sheet materials used as thermal insulating material have reflectivity and emissivity.
Correct : B. high, low
48. Thermal insulation of roofs can be obtained by covering the top exposed surface of the roof with
Correct : B. 2.5 cm thick layer of coconut pitch cement concrete
49. Presence of moisture in the thermal insulating material increases thermal insulation while the presence of air spaces decreases thermal insulation.
Correct : B. false
50. According to the Indian Standards, it is recommended that thermal damping of a wall should not be less than
Correct : C. 60%
51. According to Indian Standards, overall thermal transmittance of a wall should not be more than kcal/m2 h deg C.
Correct : B. 2.2
52. What is solar water heater?
Correct : A. use solar energy to heat water
53. Which of the following determines complexity and size of solar water heating system?
Correct : B. changes in ambient temperature
54. What is freeze protection in a solar water heating system?
Correct : C. prevents damage to system due to freezing of transfer fluid
55. What are drainback systems in solar water heating system?
Correct : D. the system that drains the transfer fluid
56. How does freeze-tolerance work?
Correct : A. by expansion of pipes carrying transfer fluid
57. Which of the following metals are used to make pipes of low cost solar water heating system?
Correct : B. copper
58. Direct solar water heating systems
Correct : C. offer no overheating protection
59. How is the heat transferred from transfer fluid to potable water in indirect solar water heating systems?
Correct : D. by using heat exchanger
60. How is water heated in a direct solar water heating system?
Correct : A. by circulating potable water through the collector
61. Passive systems rely on heat-driven convection.
Correct : B. true
62. Which of the following is an example of direct solar water heating system?
Correct : C. convection heat storage system
63. How is the heat transfer fluid (HTF) heated in bubble pump systems?
Correct : D. by subjecting the closed htf circuit to low pressure
64. Batch collectors reduce heat loss by thermally insulating the storage tank.
Correct : A. true
65. Overheat protection is done by passing hot water through collector during night.
Correct : B. true
66. As the wavelength of the radiation decreases, the intensity of the black body radiations
Correct : C. first increases then decrease
67. The radiations emitted by hot bodies are called as
Correct : B. black-body radiation
68. An iron rod is heated. The colors at different temperatures are noted. Which of the following colors shows that the iron rod is at the lowest temperature?
Correct : A. red
69. A black body is defined as a perfect absorber of radiations. It may or may not be a perfect emitter of radiations.
Correct : B. false
70. From the figure, what’s the relation between T1, T2, and T3?
Correct : B. t3 > t2 > t2
71. Electromagnetic wave theory of light could not explain Black Body radiations.
Correct : A. true
72. The unit of absorptive power is
Correct : D. no unit
73. For an object other than a black body, it’s emissivity, e is
Correct : B. 0 < e < 1
74. What relation between emissivity, e, and Absorptive Power, a, is given by Kirchhoff’s law?
Correct : C. e = a
75. What is the relation between the Energies as shown in the figure?
Correct : A. er = 0
76. The energy emitted by a black surface should not vary in accordance with
Correct : D. time
77. 2 PLANCK'S THEORY (DERIVATION)
Correct : B. a cos α
78. Likewise the amount of emitted radiation is strongly influenced by the wavelength even if temperature of the body is
Correct : A. constant
79. 5 kW/m2. Determine the wavelength of emission maximum
Correct : D. 5.46 micron m
80. The sun emits maximum radiation of 0.52 micron meter. Assuming the sun to be a black body, Calculate the emissive ability of the sun’s surface at that temperature
Correct : C. 5.47 * 10 7 w/m2
81. The law governing the distribution of radiant energy over wavelength for a black body at fixed temperature is referred to as
Correct : B. planck’s law
82. The Planck’s constant h has the dimensions equal to
Correct : A. m l 2 t -1
83. A furnace emits radiation at 2000 K. Treating it as a black body radiation, calculate the monochromatic radiant flux density at 1 micron m wavelength
Correct : D. 2.81 * 10 7 w/m2
84. A metal sphere of surface area 0.0225 m2 is in an evacuated enclosure whose walls are held at a very low temperature. Electric current is passed through resistors embedded in the sphere causing electrical energy to be dissipated at the rate of 75 W. If the sphere surfaces temperature is measured to be 560 K, while in steady state, calculate emissivity of the sphere surface
Correct : B. 0.598
85. Which of the following is the characteristic of a black body?
Correct : C. a perfect radiator and a perfect absorber
86. The energy distribution is not uniform for any given temperature in a perfect black body.
Correct : A. true
87. Rayleigh-Jean’s law holds good for which of the following?
Correct : B. longer wavelength
88. Wien’s displacement law holds good only for shorter wavelength.
Correct : B. true
89. Which of the following does not affect the photon?
Correct : A. magnetic or electric field
90. What is Compton shift?
Correct : D. shift in wavelength
91. Compton shift depends on which of the following?
Correct : C. angle of scattering
92. Which of the following is called as non- mechanical waves?
Correct : B. electromagnetic waves
93. Which of the following is associated with an electron microscope?
Correct : A. matter waves
94. A radio station broadcasts its programme at 219.3 metre wavelength. Determine the frequency of radio waves if velocity of radio waves is 3×108 m/s.
Correct : C. 1.368×106 hz
95. Calculate the de-Broglie wavelength of an electron which has been accelerated from rest on application of potential of 400volts.
Correct : C. 0.6135 Å
96. When a pebble is dropped into a pond of still water, what happens?
Correct : B. waves move
97. Mechanical waves are called elastic waves.
Correct : A. true
98. What are the essential properties a medium must possess for the propagation of mechanical waves?
Correct : D. minimum friction
99. Transverse waves can be formed in fluids.
Correct : B. false
100. Which of the following waves can be transmitted through solids, liquids and gases?