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
Direct arc furnaces have which of the following power factors ?
(A) Unity
(B) Low, lagging
(C) Low, leading
(D) Any of the above
Which of the following is an advantage of eddy current heating ?
(A) The amount of heat generated can be controlled accurately
(B) Heat at very high rate can be gene-rated
(C) The area of the surface over which heat is produced can be accurately controlled
(D) All of the above
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
For radiant heating around 2250°C, the heating elements are made of____________?
(A) copper alloy
(B) carbon
(C) tungsten alloy
(D) stainless steel alloy
The electrode of a direct arc furnace is made of____________?
(A) tungsten
(B) graphite
(C) silver
(D) copper
In direct arc furnace, which of the following has high value ?
(A) Current
(B) Voltage
(C) Power factor
(D) All of the above
In a domestic cake baking oven the temperature is controlled by________________?
(A) voltage variation
(B) thermostat
(C) auto-transformer
(D) series-parallel operation
Due to which of the following reasons it is desirable to have short arc length ?
(A) To achieve better heating
(B) To increase the life of roof refractory
(C) To have better stirring action
(D) To reduce problem of oxidation
(D) All of the above
In an electric press mica is used_____________?
(A) as an insulator
(B) as a device for power factor improvement
(C) for dielectric heating
(D) for induction heating