Electrical Heating MCQ PDF

1. A perfect black body is one which

(a) absorbs all incident radiations.
(b) reflects all incident radiations.
(c) transmits all incident radiations.
(d) all of the above.

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2. For the transmission of heat from one body to another it is essential that

(a) both bodies are solids.
(b) the two bodies are at different temperatures.
(c) both bodies are in contact.
(d) at least one of the bodies has some source of heating.

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3. Heat is transferred simultaneously by conduction, convection and radiation

(a) during melting of ice.
(b) from refrigerator coils to refrigerator freezer.
(c) inside boiler furnaces.
(d) through the surface of the insulated pipe carrying steam.

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4. The highest value of thermal conductivity is for

(a) aluminium.
(b) brass.
(c) copper.
(d) iron.

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5 The highest value of thermal conductivity is for

(a) steam.
(b) water.
(c) melting ice.
(d) solid ice.

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6. The thermal conductivity will be highest in case of

(a) dry concrete.
(b) concrete having 10% moisture by volume.
(c) concrete having 0.4% reinforcement.
(d) concrete having 10% moisture by volume and 0.4% reinforcement.

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7. Radiations from a black body are proportional to

(a) T2
(b) T3
(c) T4
(d) 1/T4

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8. A body reflecting entire radiations incidenting on it is called the

(a) white body.
(b) gray body.
(c) black body.
(d) transparent body.

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9. The insulating material suitable for low temperature applications is

(a) cork.
(b) diatomaceous earth.
(c) asbestos paper.
(d) 75 percent magnesia.

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10. The quantity of heat absorbed from the heater by convection depends upon

(a) the temperature of heating element above the surroundings.
(b) the surface area of the heater.
(c) the position of the heater.
(d) all of the above.

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11.The material of the heating element should be

(a) such that it may withstand the required temperature without getting oxidized.
(b) of low resistivity.
(c) of low melting point.
(d) of high temperature coefficient.

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12. The material to be used for heating element should be of high resistivity so as to

(a) increase the life of the heating element.
(b) reduce the length of the heating element.
(c) reduce the effect of oxidation.
(d) produce large amount of heat.

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13. The material to be used for heating element should be of low temperature coefficient so as to

(a) avoid initial rush of current.
(b) avoid change in kW rating with temperature.
(c) reduce the effect of oxidation.
(d) both (a) and (b) above.

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14. Which of the following heating element will have the least temperature range ?

(a) Eureka.
(b) Silicon carbon.
(c) Nichrome.
(d) Kanthal.

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15. Which of the following heating element can give highest temperature in resistance heating ?

(a) Nichrome.
(b) Silicon carbide.
(c) Copper.
(d) Nickel-Cr-Fe alloy.

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16. Ni-Cr-Fe alloy wires can be safely used for temperatures up to

(a) 2,500°C
(b) 2,000°C
(c) 1,150°C
(d) 850°C

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17. The heating element to be used in a furnace employed for heating around, 1,600°C should be of material

(a) nichrome.
(b) eureka.
(c) molybdenum.
(d) silicon-carbide.

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18. For radiant heating around 2,000°C the heating elements used should be of material

(a) tungsten alloy.
(b) copper alloy.
(c) carbon.
(d) stainless steel

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19. The heating element to be used in vacuum furnaces should be of the material

(a) molybdenum because of high vapor pressure.
(b) tungsten because of low vapor pressure.
(c) molybdenum because of low vapor pressure.
(d) tungsten because of high vapor pressure.

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20. In an electric press, mica is used

(a) for induction heating.
(b) for dielectric heating.
(c) as an insulator.
(d) for improvement of power factor.

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