Electrical Heating MCQ PDF

21. Maximum operating voltage is limited

(a) to 600 V.
(b) from safety consideration.
(c) by electrical insulation at high temperatures.
(d) all of the above.

22. The heat produced in the heating element(s) is also to overcome the losses occurring because of

(a) heat used in raising the temperature of oven (or furnace) and container (or carriers).
(b) heat conducted through the walls.
(c) escapement of heat due to opening of door.
(d) all of the above.

23. In a resistance furnace, the temperature is controlled by

(a) variation of operating voltage.
(b) variation of resistance of heating circuit.
(c) switching on and off the supply periodically.
(d) all of the above.

24. For temperature control in resistance furnaces resistance variation can be affected by connecting resistance elements in

(a) series.
(b) parallel.
(c) series parallel.
(d) star or delta.
(e) any of the above.

24.The simplest and most commonly used method for temperature control is

(a) external series resistance in the heating circuit.
(b) change of connections of heating circuit.
(c) use of variable number of heating elements.
(d) transformer tappings.

25. The device necessarily used for automatic temperature control in a furnace is

(a) thermostat.
(b) auto-transformer.
(c) thermocouple.
(d) any of the above.

26. Control of power input to salt-bath furnace is affected by

(a) varying the depth of immersion of electrodes.
(b) varying the distance between the electrodes.
(c) both (a) and (b).
(d) none of (a) and (b).

27 The temperature inside a furnace is usually measured by

(a) mercury thermometer.
(b) optical pyrometer.
(c) alcohol thermometer.
(d) any of the above.

28. In a resistance furnace the atmosphere is

(a) oxidizing.
(b) deoxidizing.
(c) reducing.
(d) neutral.

29. On increasing the thickness of refractory walls of the furnace

(a) energy consumption will increase.
(b) heat loss through furnace walls will increase.
(c) temperature on the outer surface of furnace walls will drop.
(d) temperature inside the furnace will drop.

30. Radiant heating is used for

(a) melting of ferrous metals.
(b) annealing of metals.
(c) drying of paints and varnishes.
(d) any of the above.

31. Direct resistance heating is used in

(a) electrode boiler.
(b) salt-bath furnace.
(c) resistance welding.
(d) all of the above.

32. Resistance ovens are used for

(a) domestic and commercial heating.
(b) vulcanizing and hardening of synthetic materials.
(c) drying of varnish coatings, drying and baking of potteries.
(d) all of the above.

33. The function(s) of an heating chamber is are to

(a) store as much of the heat supplied as may be practicable and economical.
(b) confine the atmosphere around the charge.
(c) control the cooling rate of the charge (if required) and control the distribution of heat within the chamber.
(d) all of the above.

34. For obtaining best results, the infrared lamps should be located from the object to be heated at distance of

(a) 10 – 20 cm.
(b) 25 – 30 cm.
(c) 40 – 50 cm.
(d) 50 – 60 cm.

35. In direct arc furnace which of the following is of high value ?

(a) Current.
(b) Voltage.
(c) Power factor.
(d) all of the above.

36. The power factor at which the direct arc furnace operates is

(a) low lagging.
(b) low leading.
(c) unity.
(d) high leading.

37. For arc heating the electrodes used are made of

(a) copper.
(b) graphite.
(c) tungsten.
(d) aluminum.

38. In an arc furnace, the choke is provided to

(a) reduce the surge severity.
(b) stabilize the arc.
(c) improve the power factor.
(d) all of the above.

39. It is desirable to operate the arc furnaces at a power factor of

(a) zero.
(b) unity.
(c) 0.707 lagging.
(d) 0.707 leading.

40. It is desirable to keep the arc length short in order to

(a) have better heating.
(b) have better stirring action and reduce oxidation problem.
(c) increase the life of roof refractory.
(d) all of the above.