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1) Thermal diffusivity of a substance is __________________? a. directly proportional to thermal con¬ductivity b. inversely proportional to density of substance c. inversely proportional to specific heat d. all of the above e. none of the above
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2) The thermal diffusivities for gases are generally_____________________? a. more than those for liquids b. less than those for liquids c. more than those for solids d. dependent on the viscosity e. same as for the liquids
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3) A grey body is one whose absorptivity _________________? a. varies with temperature b. varies with the wave length of incident ray c. varies with both d. does not vary with temperature and wave length of the incident ray e. there is no such criterion
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4) Planck’s law holds good for________________? a. black bodies b. polished bodies c. all coloured bodies d. all of the above e. none of the above
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5) A perfect black body is one which_______________? a. is black in colour b. reflects all heat c. transmits all heat radiations d. abslprbs heat radiations of all wave lengths falling on it e. fully opaque
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6) If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of___________________? a. 3 b. 6 c. 9 d. 27 e. 81
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7) In regenerator type heat exchanger, heat transfer takes place by___________________? a. direct mixing of hot and cold fluids b. a complete separation between hot and cold fluids c. flow of hot and cold fluids alternately over a surface d. generation of heat again and again e. indirect transfer
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8) Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by ___________________? a. convection b. free convection c. forced convection d. radiation e. radiation and convection
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9) Depending on the radiating properties, body will be transparent when________________? a. p = 0, x = 0 and a = 1 b. p=l,x = 0,anda = 0 c. p = 0, T= l,anda = 0 d. X = 0, a + p = 1 e. a = 0,x + p= 1
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10) Absorptivity of a body will be equal to its emissivity___________________? a. at all temperatures b. at one particular temperature c. when system is under thermal equi-librium d. at critical temperature e. for a polished body
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11) The amount of radiation mainly depends on___________________? a. nature of body b. temperature of body c. type of surface of body d. all of the above e. none of the above
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12) The ratio of the energy absorbed by the body to total energy falling on it is called_________________? a. absorptive power b. emissive power c. absorptivity d. emissivity e. none of the above
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13) The emissive power of a body depends upon its___________________? a. temperature b. wave length c. physical nature d. all of the above e. none of the above
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14) 40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is____________________? a. 0.45 b. 0.55 c. 0.40 d. 0.75 e. 0.60
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15) The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit_______________? a. temperature b. thickness c. area d. time e. area and time
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16) Depending on the radiating properties, a body will be black when_________________? a. p = 0, x = 0 and a = 1 b. p= l,T = 0anda = 0 c. p = 0, x = 1 and a = 0 d. x = 0, a + p = 0 e. a = 0,x + p= 1.
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17) According to Stefan’s law, the total radiation from a black body per second per unit area is proportional to____________________? a. absolute temperature b. T2 c. T5 d. t e. l/T
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18) The thermal diffusivities for solids are generally__________________? a. less than those for gases b. less than those for liquids c. more than those for liquids and gases d. more or less same as for liquids and gases e. zerci
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19) The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as_________________? a. Krichoff’s law b. Stefan’s law c. Wien’ law d. Planck’s law e. Black body law
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20) Depending on the radiating properties, a body will be white when_________________? a. p = 0, x = 0 and a = 1 b. p=l,T = 0anda = 0 c. p = 0, x = 1 and a = 0 d. x = 0, a + p = 1 e. a = 0, x + p = 1.
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21) Depending on the radiating properties, a body will be opaque when _________________? a. p = 0, x = 0 and a = 1 b. p=l,x = 0anda = 0 c. p = 0, x = 1 and a = 0 d. x – 0, a + p = 1 e. a=0,x + p= 1.
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22) According to Wien’s law, the wavelength corresponding to maximum energy is proportion to ________________? a. absolute temperature (T) b. I2 c. f d. t e. 1/r
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