Heat Transfer

51. The emissive power of a body depends upon its

1. temperature
2. wave length
3. physical nature
4. all of the above
5. none of the above.

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52. The energy distribution of an ideal reflector at higher temperatures is largely in the range of

1. shorter wavelength
2. longer wavelength
3. remains same at all wavelengths
4. wavelength has nothing to do with it
5. none of the above.

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53. The insulation ability of an insulator with the presence of moisture would

1. increase
2. decrease
3. remain unaffected
4. may increase/decrease depending on temperature and thickness of insulation
5. none of the above.

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54. The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as

1. emissivity
2. transmissivity
3. reflectivity
4. intensity of radiation
5. absorptivity.

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55. The ratio of heat flow Q1/Q2 from two walls of same thickness having their thermal conductivities as ATj – 2K2 will be

1. I
2. 0.5
3. 2
4. 0.25
5. 4

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56. 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

1. Krichoff's law
2. Stefan's law
3. Wien' law
4. Planck's law
5. Black body law.

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57. The ratio of the energy absorbed by the body to total energy falling on it is called

1. absorptive power
2. emissive power
3. absorptivity
4. emissivity
5. none of the above.

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58. The thermal diffusivities for gases are generally

1. more than those for liquids
2. less than those for liquids
3. more than those for solids
4. dependent on the viscosity
5. same as for the liquids.

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59. The thermal diffusivities for solids are generally

1. less than those for gases
2. jess than those for liquids
3. more than those for liquids and gases
4. more or less same as for liquids and gases
5. zerci.

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60. The time constant of a thermocouple is

1. the time taken to attain the final temperature to be measured
2. the time taken to attain 50% of the value of initial temperature difference
3. the time taken to attain 63.2% of the value of initial temperature difference
4. determined by the time taken to reach 100°C from 0°C
5. none of the above.

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