Heat Transfer

21. Depending on the radiating properties, a body will be white when

  1. p = 0, x = 0 and a = 1
  2. p=l,T = 0anda = 0
  3. p = 0, x = 1 and a = 0
  4. x = 0, a + p = 1
  5. a = 0, x + p = 1.

Correct answer: (B)
p=l,T = 0anda = 0

22. Emissivity of a white polished body in comparison to a black body is

  1. higher
  2. lower
  3. same
  4. depends upon the shape of body
  5. none of the above.

Correct answer: (B)
lower

23. Film coefficient is defined as Inside diameter of tube

  1. Equivalent thickness of film
  2. Thermal conductivity Equivalent thickness of film Specific heat x Viscocity
  3. Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity
  4. Film coefficient x Inside diameter Thermalconductivity
  5. none of the above.

Correct answer: (B)
Thermal conductivity Equivalent thickness of film Specific heat x Viscocity

24. Fourier's law of heat conduction is valid for

  1. one dimensional cases only
  2. two dimensional cases only
  3. three dimensional cases only
  4. regular surfaces having non-uniform temperature gradients
  5. irregular surfaces.

Correct answer: (A)
one dimensional cases only

25. Heat conducted througfi unit area and unit thick face per unit time when temperature difference between opposite faces is unity,is called

  1. thermal resistance
  2. thermal coefficient
  3. temperature gradient
  4. thermal conductivity
  5. heat-transfer.

Correct answer: (D)
thermal conductivity

26. Heat flows from one body to other when they have

  1. different heat contents
  2. different specific heat
  3. different atomic structure
  4. different temperatures
  5. none of the above.

Correct answer: (D)
different temperatures

27. Heat is closely related with

  1. liquids
  2. energy
  3. temperature
  4. entropy
  5. enthalpy.

Correct answer: (C)
temperature

28. Heat is transferred by all three modes of transfer, viz, conduction, convection and radiation in

  1. electric heater
  2. steam condenser
  3. melting of ice
  4. refrigerator condenser coils
  5. boiler.

Correct answer: (E)
boiler.

29. Heat transfer by radiation mainly depends upon

  1. its temperature
  2. nature of the body
  3. kind and extent of its surface
  4. all of the above
  5. none of the above.

Correct answer: (D)
all of the above

30. Heat transfer in liquid and gases takes place by

  1. conduction
  2. convection
  3. radiation
  4. conduction and convection
  5. convection and radiation.

Correct answer: (B)
convection

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