mechanical engineering MCQs – Page 153

Practise multiple-choice questions from mechanical engineering for competitive examinations and subject revision. Review each marked answer and report any item that may be outdated or unclear.

mechanical engineering Mcqs

1. compressors gas turbines and jet engines 2. theory of machines 3. nuclear power plants 4. engineering materials 5. strength of materials mechanical engineering 6. thermodynamics 7. heat transfer 8. i c engines 9. steam boilers engines nozzles and turbines 10. engineering mechanics 11. fluid mechanics mechanical engineering 12. production technology 13. machine design 14. hydraulic machines 15. workshop technology 16. refrigeration and air conditioning

3041. Total heat is the heat required to__________________?
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A. convert water into steam and superheat it

B. increase the temperature of a liquid or vapour

C. change liquid into vapour

D. change vapour into liquid

E. convert saturated steam into dry steam

3042. According to Prevost theory of heat exchange ___________________?
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A. all bodies above absolute zero emit radiation

B. it is impossible to transfer heat from low temperature source to t high temperature source

C. rate of heat transfer depends on thermal conductivity and temperature difference

D. heat transfer by radiation requires no medium

E. heat transfer in most of the cases takes place by combination of conduction, convection and radiation

3043. Heat transfer by radiation mainly depends upon___________________?
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A. nature of the body

B. none of the above

C. its temperature

D. kind and extent of its surface

E. all of the above

3044. Two balls of same material and finish have their diameters in the ratio of 2 : 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of____________________?
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A. 1:01

B. 1:04

C. 2:01

D. 1 : 2

E. 4:01

3045. The time constant of a thermocouple is_______________?
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A. determined by the time taken to reach 100C from 0C

B. none of the above

C. the time taken to attain 63.2% of the value of initial temperature difference

D. the time taken to attain 50% of the value of initial temperature difference

E. the time taken to attain the final temperature to be measured

3046. Cork is a good insulator because it has___________________?
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A. porous body

B. free electrons

C. low density

D. all of the above

E. atoms colliding frequency

3047. Unit of thermal diffusivity is_________________?
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A. kcal/m2 hrC

B. m2/hr

C. m2/hrC

D. kcal/m.hrC

E. kcal/m2 hr

3048. Heat flowing from one side to other depends directly on ___________________?
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A. k up the wrong case?

3049. Fouriers law of heat conduction is valid for_________________?
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A. regular surfaces having non-uniform temperature gradients

B. two dimensional cases only

C. one dimensional cases only

D. three dimensional cases only

E. irregular surfaces

3050. Heat is closely related with___________________?
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A. liquids

B. enthalpy

C. entropy

D. energy

E. temperature

3051. According of Kirchhoffs law______________________?
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A. emissive power and absorptivity are constant for all bodies

B. ratio of emissive power to absorptive power is maximum for perfectly black body

C. ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body

D. radiant heat is proportional to fourth power of absolute temperature

E. emissive power depends on temperature

3052. Which of the following has maximum value of thermal conductivity________________?
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A. brass

B. aluminium

C. lead

D. copper

E. steel

3053. Unit of thermal conductivity in S.I. units is__________________?
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A. B. and C. above

B. J/m K sec

C. J/m2 sec

D. A. and C. above

E. W/m K

3054. In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by___________________?
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A. convection

B. radiation

C. conduction

D. both convection and conduction

E. none of the above

3055. Heat transfer in liquid and gases takes place by_____________________?
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A. conduction and convection

B. radiation

C. convection

D. convection and radiation

E. conduction

3056. Moisture would find its way into insulation by vapour pressure unless it is prevented by __________________ ?
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A. less thermal conductivity insulator

B. all of the above

C. high thickness of insulation

D. high vapour pressure

E. a vapour seal

3057. Thermal conductivity of wood depends on_______________?
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A. all of the above

B. density

C. none of the above

D. temperature

E. moisture

3058. Which of the following has least value of conductivity_________________?
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A. glass

B. air

C. plastic

D. rubber

E. water

3059. A grey body is one whose absorptivity_________________?
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A. varies with temperature

B. does not vary with temperature and. wavelength of the incident ray

C. varies with wavelength of the incident ray

D. is equal to its emissivity

E. none of the above

3060. Thermal conductivity of solid metals with rise in temperature normally___________________?
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A. increases

B. unpredictable

C. remains constant

D. decreases

E. may increase or decrease depending on temperature

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