Electrical Power Engineering Multiple Choice Questions and Answers (MCQs) Part 3:
102. The most suitable motor for a steel mill requiring a motor having high starting torque, wide speed range and precise speed control is
(a) plain squirrel cage induction motor.
(b) wound rotor induction motor.
(c) dc series motor.
(d) dc shunt motor.
Answer : (c) dc series motor.
103. For automatic drives the preference is for
(a) synchronous motors.
(b) Ward-Leonard controlled dc shunt motors.
(c) plain squirrel cage induction motors.
Answer : (b) Ward-Leonard controlled dc shunt motors.
104. The type of motor that can be used for hoisting machinery is
(a) dc compound motor.
(b) Ward-Leonard controlled dc shunt motor.
(c) wound rotor induction motor.
(d) any of the above.
Answer : (d) any of the above.
105. The motor normally used for crane travel is
(a) wound rotor induction motor.
(b) synchronous motor.
(c) dc differentially compounded motor.
(d) plain squirrel cage induction motor.
Answer : (d) plain squirrel cage induction motor.
106. The drive, that can be used for derricks and winches is
(a) pole-changing squirrel cage induction motor.
(b) ac slip-ring induction motor with variable resistance.
(c) dc shunt motor with Ward-Leonard control.
(d) any of the above
Answer : (d) any of the above
107. Ward-Leonard controlled dc drives are generally used for ………. duty excavators
(a) light
(b) medium
(c) heavy
(d) none of these.
Answer : (c) heavy
108. The motor suitable for a reciprocating pump required to start under load is
(a) plain squirrel cage induction motor.
(b) double-squirrel cage induction motor.
(c) synchronous motor.
(d) dc shunt motor.
Answer : (b) double-squirrel cage induction motor.
109. A pole-changing squirrel cage induction motor employed in derricks has four, eight and twenty four poles. The lowest speed is used in
(a) hoisting.
(b) landing the load.
(c) lifting.
(d) lowering.
Answer : (b) landing the load.
110. A pole-changing type squirrel cage induction motor employed in derricks has four, eight and twenty four poles. The medium speed is used in
(a) landing the load.
(b) hoisting.
(c) lowering.
(d) lifting.
Answer : (d) lifting.
111. Motor preferred for kiln drive is usually
(a) wound rotor induction motor.
(b) cascaded controlled ac motor.
(c) Ward-Leonard controlled dc shunt motor.
(d) any of the above.
Answer : (d) any of the above.
112. The motor used in mines is
(a) flame-proof squirrel cage induction or wound rotor motor.
(b) dc series motor.
(c) dc shunt motor.
(d) any of the above.
Answer : (a) flame-proof squirrel cage induction or wound rotor motor.
113. The motor used in punches, presses and shears is
(a) dc series or shunt motors.
(b) dc cumulative compound motor.
(c) high slip squirrel cage or wound rotor induction motor.
(d) both (b) and (c).
Answer : (d) both (b) and (c).
114. A domestic mixer uses the following motor
(a) induction motor.
(b) reluctance motor.
(c) universal motor.
(d) permanent magnet synchronous motor.
Answer : (c) universal motor.
115. 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.
Answer : (a) absorbs all incident radiations.
116. For the transmission of heat from one body to another it is essenÂtial 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.
Answer : (b) the two bodies are at different temperatures.
117. 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.
Answer : (c) inside boiler furnaces.
118. The highest value of thermal conductivity is for
(a) aluminium.
(b) brass.
(c) copper.
(d) iron.
Answer : (c) copper.
119. The highest value of thermal conductivity is for
(a) steam.
(b) water.
(c) melting ice.
(d) solid ice.
Answer : (d) solid ice.
120. 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% reinÂforcement.
Answer : (d) concrete having 10% moisture by volume and 0.4% reinÂforcement.
121. Radiations from a black body are proportional to
(a) T2
(b) T3
(c) T4
(d) 1/T4
Answer : (c) T4
122. A body reflecting entire radiations incidenting on it is called the
(a) white body.
(b) gray body.
(c) black body.
(d) transparent body.
Answer : (a) white body.
123. The insulating material suitable for low temperature applications is
(a) cork.
(b) diatomaceous earth.
(c) asbestos paper.
(d) 75 per cent magnesia.
Answer : (b) diatomaceous earth.
124. The quantity of heat absorbed from the heater by convection deÂpends 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.
Answer : (d) all of the above.
125. The material of the heating element should be
(a) such that it may withstand the required temperature without getting oxidised.
(b) of low resistivity.
(c) of low melting point.
(d) of high temperature coefficient.
Answer : (a) such that it may withstand the required temperature without getting oxidised.
126. 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.
Answer : (b) reduce the length of the heating element.
127. 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.
Answer : (d)both (a) and (b) above.
128. Which of the following heating element will have the least temperature range ?
(a) Eureka.
(b) Silicon carbon.
(c) Nichrome.
(d) Kanthal.
Answer : (a) Eureka.
129. 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.
Answer : (b) Silicon carbide.
130. 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
Answer : (d) 850°C
131. 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.
Answer : (c) molybdenum.
132. For radiant heating around 2,000°C the heating elements used should be of material
(a) tungsten alloy.
(b) copper alloy.
(c) carbon.
(d) Stenleess.
Answer : (a) tungsten alloy.
133. The heating element to be used in vacuum furnaces should be of the material
(a) molybdenum because of high vapour pressure.
(b) tungsten because of low vapour pressure.
(c) molybdenum because of low vapour pressure.
(d) tungsten because of high vapour pressure.
Answer : (b) tungsten because of low vapour pressure.
134. 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.
Answer : (c) as an insulator.
135. 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.
Answer : (d) all of the above.
136. 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.
Answer : (d) all of the above.
137. 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.
Answer : (d) all of the above.
138. 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.
Answer : (e) any of the above.
139. 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) transfomer tappings.
Answer : (b) change of connections of heating circuit.
140. The device necessarily used for automatic temperature control in a furnace is
(a) thermostat.
(b) auto-transformer.
(c) thermocouple.
(d) any of the above.
Answer : (a) thermostat.
141. 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).
Answer : (c) both (a) and (b).
142. The temperature inside a furnace is usually measured by
(a) mercury thermometer.
(b) optical pyrometer.
(c) alcohol thermometer.
(d) any of the above.
Answer : (b) optical pyrometer.
143. In a resistance furnace the atmosphere is
(a) oxidising.
(b) deoxidising.
(c) reducing.
(d) neutral.
Answer : (a) oxidising.
144. 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.
Answer : (c) temperature on the outer surface of furnace walls will drop.
145. 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.
Answer : (c) drying of paints and varnishes.
146. Direct resistance heating is used in
(a) electrode boiler.
(b) salt-bath furnace.
(c) resistance welding.
(d) all of the above.
Answer : (d) all of the above.
147. 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.
Answer : (d) all of the above.
148. 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.
Answer : (d) all of the above.
149. 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.
Answer : (b) 25-30 cm.
150. In direct arc furnace which of the following is of high value ?
(a) Current.
(b) Voltage.
(c) Power factor.
(d) all of the above.
Answer : (a) Current.
151. The power factor at which the direct arc furnace operates is
(a) low lagging.
(b) low leading.
(c) unity.
(d) high leading.
Answer : (a) low lagging.