McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .
Chapters
| 1. |
Unit of thermal conductivity in S.I. units is |
| A. | J/m2 sec |
| B. | J/m °K |
| C. | W/m °K |
| D. | (b) and (c) |
| Answer» C. W/m °K | |
| 2. |
Thermal conductivity of solid metals with rise in temperature normally |
| A. | increases |
| B. | decreases |
| C. | remains constant |
| D. | may increase or decrease depending on temperature |
| Answer» B. decreases | |
| 3. |
Heat transfer takes place as per - |
| A. | zeroth law of thermodynamics |
| B. | first law of thermodynamic |
| C. | second law of the thermodynamics |
| D. | Kirchhoff law (e) Stefan's law. |
| Answer» C. second law of the thermodynamics | |
| 4. |
When heat is transferred from one particle of hot body to another by actual motion of the heated particles, it is referred to as heat transfer by |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | conduction and convection |
| Answer» A. conduction | |
| 5. |
When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | conduction and convection |
| Answer» C. radiation | |
| 6. |
The insulation ability of an insulator with the presence of moisture would |
| A. | increase |
| B. | decrease |
| C. | remain unaffected |
| D. | may increase/decrease depending on temperature and thickness of insulation |
| Answer» B. decrease | |
| 7. |
When heat is Transferred by molecular collision, it is referred to as heat transfer by |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | convection and radiation. |
| Answer» B. convection | |
| 8. |
Heat transfer in liquid and gases takes place by |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | conduction and convection |
| Answer» B. convection | |
| 9. |
Which of the following is the case of heat transfer by radiation |
| A. | blast furnace |
| B. | heating of building |
| C. | cooling of parts in furnace |
| D. | all of the above. |
| Answer» D. all of the above. | |
| 10. |
Heat is closely related with |
| A. | liquids |
| B. | energy |
| C. | temperature |
| D. | entropy |
| Answer» C. temperature | |
| 11. |
Metals are good conductors of heat because |
| A. | their atoms collide frequently |
| B. | thier atoms-are relatively far apart |
| C. | they contain free electrons |
| D. | they have high density |
| Answer» A. their atoms collide frequently | |
| 12. |
Thermal conductivity of air with rise in temperature |
| A. | increases |
| B. | decreases |
| C. | remains constant |
| D. | may increase or decrease depending on temperature |
| Answer» A. increases | |
| 13. |
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 | |
| 14. |
The concept of overall coefficient of heat transfer is used in heat transfer problems of |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | conduction and convection. |
| Answer» D. conduction and convection. | |
| 15. |
In heat transfer, conductance equals conductivity (kcal/hr/sqm/°C/cm) divided by |
| A. | hr (time) |
| B. | sqm (area) |
| C. | °C (temperature) |
| D. | cm (thickness) |
| Answer» D. cm (thickness) | |
| 16. |
The amount of heat flow through a body by conduction is |
| A. | directly proportional to the surface area of the body |
| B. | directly proportional to the temperature gradient of the body |
| C. | dependent upon the material of the body |
| D. | all of the above. |
| Answer» D. all of the above. | |
| 17. |
Which of the following has least value of conductivity |
| A. | glass |
| B. | water |
| C. | plastic |
| D. | air |
| Answer» D. air | |
| 18. |
Which of the following is expected to have highest thermal conductivity |
| A. | steam |
| B. | solid ice |
| C. | melting ice |
| D. | water |
| Answer» B. solid ice | |
| 19. |
Thermal conductivity of a material may be defined as the |
| A. | quantity of heat flowing in one second through one cm cube of material when opposite faces are maintained at a temperature difference of 1°C |
| B. | quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C |
| C. | heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces |
| D. | all of the above |
| Answer» D. all of the above | |
| 20. |
Which of the following has maximum value of thermal conductivity |
| A. | aluminium |
| B. | steel |
| C. | brass |
| D. | copper |
| Answer» A. aluminium | |
| 21. |
Heat is transferred by all three modes of transfer (conduction, convection and radiation) in, |
| A. | electric heater |
| B. | steam condenser |
| C. | melting of ice |
| D. | boiler. |
| Answer» D. boiler. | |
| 22. |
Heat transfer by radiation mainly depends upon |
| A. | its temperature |
| B. | nature of the body |
| C. | kind and extent of its surface |
| D. | all of the above |
| Answer» D. all of the above | |
| 23. |
Thermal conductivity of wood depends on |
| A. | moisture |
| B. | density |
| C. | temperature |
| D. | all of the above |
| Answer» D. all of the above | |
| 24. |
Heat conducted through unit area and unit thick face per unit time when temperature difference between opposite faces is unity,is called |
| A. | thermal resistance |
| B. | thermal coefficient |
| C. | temperature gradient |
| D. | thermal conductivity |
| Answer» D. thermal conductivity | |
| 25. |
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 | |
| 26. |
A grey body is one whose absorptivity |
| A. | varies with temperature |
| B. | varies with wavelength of the incident ray |
| C. | is equal to its emissivity |
| D. | does not vary with temperature and wavelength of the incident ray |
| Answer» C. is equal to its emissivity | |
| 27. |
A non-dimensional number generally associated with natural convection heat transfer is |
| A. | Grashoff number |
| B. | Nusselt number |
| C. | Weber number |
| D. | Prandtl number |
| Answer» A. Grashoff number | |
| 28. |
LMTD in case of counter flow heat exchanger as compared-to parallel flow heat exchanger is |
| A. | higher |
| B. | lower |
| C. | same |
| D. | depends on the area of heat exchanger |
| Answer» A. higher | |
| 29. |
In counter flow heat exchangers |
| A. | both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state |
| B. | both the fluids at inlet are in their hottest state |
| C. | both the fluids .at exit are in their hottest state |
| D. | one fluid is in hottest state and other in coldest state at inlet |
| Answer» B. both the fluids at inlet are in their hottest state | |
| 30. |
Fourier's law of heat conduction is valid for |
| A. | one dimensional cases only |
| B. | two dimensional cases only |
| C. | three dimensional cases only |
| D. | regular surfaces having non-uniform temperature gradients |
| Answer» A. one dimensional cases only | |
| 31. |
All radiations in a black body are |
| A. | reflected |
| B. | partly reflected and partly absorbed |
| C. | transmitted |
| D. | absorbed |
| Answer» D. absorbed | |
| 32. |
According to Kirchoff's law, ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a |
| A. | grey body |
| B. | brilliant white polished body |
| C. | red hot body |
| D. | black body |
| Answer» D. black body | |
| 33. |
The unit of overall coefficient of heat transfer is |
| A. | W/m2 |
| B. | W/°C |
| C. | W/m2 °C |
| D. | W/m °C |
| Answer» C. W/m2 °C | |
| 34. |
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. | cube of absolute temperature. |
| Answer» C. fourth power of absolute temperature | |
| 35. |
The unit of Stefan Boltzmann constant is |
| A. | watt/cm2 °K |
| B. | watt/cm4 °K |
| C. | watt2/cm °K4 |
| D. | watt/cm2 °K4 |
| Answer» D. watt/cm2 °K4 | |
| 36. |
Stefan Boltzmann law is applicable for heat transfer by |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | conduction and radiation combined |
| Answer» C. radiation | |
| 37. |
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 |
| A. | Krichoff's law |
| B. | Stefan's law |
| C. | Wien' law |
| D. | Planck's law |
| Answer» A. Krichoff's law | |
| 38. |
The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit |
| A. | temperature |
| B. | thickness |
| C. | area |
| D. | time |
| Answer» D. time | |
| 39. |
The ratio of the energy absorbed by the body to total energy falling on it is called |
| A. | absorptive power |
| B. | emissive power |
| C. | absorptivity |
| D. | emissivity |
| Answer» A. absorptive power | |
| 40. |
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 absorptivity of surface is |
| A. | 0.45 |
| B. | 0.55 |
| C. | 0.40 |
| D. | 0.75 |
| Answer» A. 0.45 | |
| 41. |
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 | |
| 42. |
The emissive power of a body depends upon its |
| A. | temperature |
| B. | wave length |
| C. | physical nature |
| D. | all of the above |
| Answer» D. all of the above | |
| 43. |
Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by |
| A. | convection |
| B. | free convection |
| C. | forced convection |
| D. | radiation |
| Answer» D. radiation | |
| 44. |
In regenerative type heat exchanger, heat transfer takes place by |
| A. | direct mixing of hot and cold fluids |
| B. | a complete separation between hot and cold fluids |
| C. | flow of hot and cold fluids alternately over a surface |
| D. | indirect tr |
| Answer» A. direct mixing of hot and cold fluids | |
| 45. |
A perfect black body is one which |
| A. | is black in colour |
| B. | reflects all heat |
| C. | transmits all heat radiations |
| D. | absorbs heat radiations of all wave lengths falling on it |
| Answer» D. absorbs heat radiations of all wave lengths falling on it | |
| 46. |
If the temperature of a solid surface changes from 27°C to 627°C, then its emissive power changes in the ratio of |
| A. | 3 |
| B. | 81 |
| C. | 9 |
| D. | 27 |
| Answer» B. 81 | |
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