# Heat and Mass Transfer – Set 05

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(D) All of these

## Q2. If the energy radiated per second per sq. cm. of the surface for wave lengths lying between λ, and λ + dλ is represented by (eλ.dλ), then eλ is called

(A) Absorptive power
(B) Emissive power
(C) Emissivity
(D) None of these

## Q3. Film coefficient is defined as the ratio of

(A) Thermal conductivity to the equivalent thickness of the film of fluid
(B) Temperature drop through the films of fluids to the thickness of film of fluids
(C) Thickness of film of fluid to the thermal conductivity
(D) Thickness of film of fluid to the temperature drop through the films of fluids

Answer:(A) Thermal conductivity to the equivalent thickness of the film of fluid

## Q4. The rate of heat flow through a body is Q = [kA (T₁ – T₂)]/x. The term x/kA is known as

(A) Thermal coefficient
(B) Thermal resistance
(C) Thermal conductivity
(D) None of these

## Q5. The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called

(A) First law of thermodynamics
(B) Newton’s law of cooling
(C) Newton’s law of heating
(D) Stefan’s law

Answer: (B) Newton’s law of cooling

(A) 0
(B) 0.5
(C) 0.75
(D) 1

## Q7. The transfer of heat by molecular collision is smallest in

(A) Solids
(B) Liquids
(C) Gases
(D) None of these

(A) 0.45
(B) 0.55
(C) 0.40
(D) 0.75

## Q9. Heat transfer takes place as per

(A) Zeroth law of thermodynamics
(B) First law of thermodynamic
(C) Second law of the thermodynamics
(D) Kirchoff’s law

Answer: (C) Second law of the thermodynamics

## Q10. Metals are good conductors of heat because

(A) Their atoms collide frequently
(B) Their atoms are relatively far apart
(C) They contain free electrons
(D) They have high density

Answer: (A) Their atoms collide frequently

## Q11. Heat flows from one body to other when they have

(A) Different heat contents
(B) Different specific heat
(C) Different atomic structure
(D) Different temperatures

## Q12. Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in

(A) Electric heater
(B) Steam condenser
(C) Boiler
(D) Refrigerator condenser coils

## Q13. Emissivity of a white polished body in comparison to a black body is

(A) Higher
(B) Lower
(C) Same
(D) Depends upon the shape of body

(A) Reflected
(B) Refracted
(C) Transmitted
(D) Absorbed

## Q15. According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to

(A) Absolute temperature
(B) Square of temperature
(C) Fourth power of absolute temperature
(D) Fourth power of temperature

Answer:(C) Fourth power of absolute temperature

## Q16. According to Wien’s law, the wavelength corresponding to maximum energy is proportion to

(A) Absolute temperature (T)
(B) I²
(C) F
(D) T

(A) 0.1
(B) 0.23
(C) 0.42
(D) 0.51

## Q18. In heat exchangers, degree of approach is defined as the difference between temperatures of

(A) Cold water inlet and outlet
(B) Hot medium inlet and outlet
(C) Hot medium outlet and cold water inlet
(D) Hot medium outlet and cold water outlet

Answer: (D) Hot medium outlet and cold water outlet

## Q19. 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

Answer: (D) All of the above

## Q20. The heat transfer by conduction through a thick sphere is given by

(A) Q = 2πkr1 r2 (T1 – T2)/ (r2 – r1)
(B) Q = 4πkr1 r2 (T1 – T2)/ (r2 – r1)
(C) Q = 6πkr1 r2 (T1 – T2)/ (r2 – r1)
(D) Q = 8πkr1 r2 (T1 – T2)/ (r2 – r1)

Answer: (B) Q = 4πkr1 r2 (T1 – T2)/ (r2 – r1)

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