Heat and Mass Transfer – Set 05

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Q1. The radiation emitted by a black body is known as

(A) Black radiation
(B) Full radiation
(C) Total radiation
(D) All of these

Answer: (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

Answer: (B) Emissive power


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

Answer: (B) Thermal resistance


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


Q6. The emissivity for a black body is

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

Answer: (D) 1


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

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

Answer: (C) Gases


Q8. 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

Answer: (A) 0.45


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

Answer: (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

Answer: (C) Boiler


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

Answer: (B) Lower


Q14. All radiations in a black body are

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

Answer: (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

Answer: (A) Absolute temperature (T)


Q17. Thermal conductivity of water at 20°C is of the order of

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

Answer:(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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Heat and Mass Transfer – Set 01
Heat and Mass Transfer – Set 02
Heat and Mass Transfer – Set 03
Heat and Mass Transfer – Set 04
Heat and Mass Transfer – Set 05
Heat and Mass Transfer – Set 06
Heat and Mass Transfer – Set 07
Heat and Mass Transfer – Set 08