Heating and Welding

41. Resistance variation method of temperature control is done by connecting resistance elements in

1. series
2. parallel
3. series-parallel connections
4. star-delta connections
5. all of the above ways

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42. Hysteresis loss and eddy current loss are used in

1. induction heating of steel
2. dielectric heating
3. induction heating of brass
4. resistance heating

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43. In heating the ferromagnetic material by induction heating, heat is produced due to

1. induced current flow through the charge
2. hysteresis loss taking place below curie temperature
3. due to hysteresis loss as well as eddy current loss takingplace in the charge
4. none of the above factors

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44. Radiant heating is used for which of the following?

1. Annealing of metals
2. Melting of ferrous metals
3. Heating of liquids in electric kettle
4. Drying of paints and varnishes

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45. Which of the following devices is necessarily required for automatic temperature control in a furnace?

1. Thermostat
2. Thermocouple
3. Auto-transformer
4. Heating elements of variable resis-tance material

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46. For radiant heating around 2250°C, the heating elements are made of

1. copper alloy
2. carbon
3. tungsten alloy
4. stainless steel alloy

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47. Which of the following is an advantage of eddy current heating?

1. The amount of heat generated can be controlled accurately
2. Heat at very high rate can be gene-rated
3. The area of the surface over which heat is produced can be accurately controlled
4. All of the above

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48. The electrode of a direct arc furnace is made of

1. tungsten
2. graphite
3. silver
4. copper

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49. Direct arc furnaces have which of the following power factors?

1. Unity
2. Low, lagging
3. Low, leading
4. Any of the above

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50. In direct arc furnace, which of the following has high value?

1. Current
2. Voltage
3. Power factor
4. All of the above

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