1. ______ method has leading power factor
(a) Resistance heating
(b) Dielectric heating
(c) Arc heating
(d) Induction heating
Ans: b
2. Heat is transferred simultaneously by condition, convection and radiation
(a) inside boiler furnaces
(b) during melting of ice
(c) through the surface of the insulted pipe carrying steam
(d) from refrigerator coils to freezer of a refrigerator
Ans: a
3. The process of heat transfer during the reentry of satellites and missiles, at very high speeds, into earth’s atmosphere is known as
(a) ablation
(b) radiation
(c) viscous dissipation
(d) irradiation
Ans: a
4. Which of the following has the highest value of thermal conductivity ?
(a) Water
(b) Steam
(c) Solid ice
(d) Melting ice
Ans: c
5. Which of the following insulating materials was suitable for low temperature applications ?
(a) Asbestos paper
(b) Diatomaceous earth
(c) 80 percent magnesia
(d) Cork
Ans: b
6. Which of the following will happen if the thickness of refractory wall of furnace is increased ?
(a) Heat loss through furnace wall will increase
(b) Temperature inside the furnace will fall
(c) Temperature on the outer surface of furnace walls will drop
(d) Energy consumption will increase
Ans: c
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7. In a resistance furnace the atmosphere is
(a) oxidising
(b) deoxidising
(c) reducing
(d) neutral
Ans: a
8. By the use of which of the following, high frequency power supply for induction furnaces can be obtained ?
(a) Coreless transformers
(b) Current transformers
(c) Motor-generator set
(d) Multi-phase transformer
Ans: c
9. In an electric room heat convector the method of heating used is
(a) arc heating
(b) resistance heating
(c) induction heating
(d) dielectric heating
Ans: b
10. In a domestic cake baking oven the temperature is controlled by
(a) voltage variation
(b) thermostat
(c) auto-transformer
(d) series-parallel operation
Ans: d
11. In resistance heating highest working temperature is obtained from heating elements made of
(a) nickel copper
(b) nichrome
(c) silicon carbide
(d) silver
Ans: c
12. In the indirect resistance heating method, maximum heat-transfer takes place by
(a) radiation
(b) convection
(c) conduction
(d) any of the above
Ans: a
13. Property of low temperature co-efficient of heating element is desired due to which of the following reasons ?
(a) To avoid initial rush of current
(b) To avoid change in kW rating with temperature
(c) Both (a) and (b)
(d) Either (a) or (b)
Ans: c
14. Radiations from a black body are proportional to
(a) T1
(b) T2
(c) T3
(d) T4
Ans: d
15. Ajax Wyatt furnace is started when
(a) it is filled below core level
(b) it is filled above core level
(c) it is fully empty
(d) none of the above
Ans: b
16. Radiant heating is used for which of the following ?
(a) Annealing of metals
(b) Melting of ferrous metals
(c) Heating of liquids in electric kettle
(d) Drying of paints and varnishes
Ans: d
17. Which of the following devices is necessarily required for automatic temperature control in a furnace ?
(a) Thermostat
(b) Thermocouple
(c) Auto-transformer
(d) Heating elements of variable resis-tance material
Ans: b
18. For radiant heating around 2250°C, the heating elements are made of
(a) copper alloy
(b) carbon
(c) tungsten alloy
(d) stainless steel alloy
Ans: c
19. The electrode of a direct arc furnace is made of
(a) tungsten
(b) graphite
(c) silver
(d) copper
Ans: b
20. In direct arc furnace, which of the following has high value ?
(a) Current
(b) Voltage
(c) Power factor
(d) All of the above
Ans: a
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