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McqMate
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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