Electrical Power Engineering Multiple Choice Questions and Answers (MCQs) Part 5:
202. In resistance welding, the magnitude of current is controlled
(a) by varying the primary voltage of the welding transformer using an auto-transformer between supply and welding transformer.
(b) by changing the primary turns of the welding transformer.
(c) by varying the magnitude and waveform of the primary as well as secondary current by using thyratron or ignitron.
(d) any of the above.
Answer : (d) any of the above.
203. The main drawback of resistance welding is
(a) high initial as well as maintenance cost.
(b) difficult shapes and sections cannot be welded.
(c) only similar metals can be welded.
(d) parent metal is affected.
Answer : (a) high initial as well as maintenance cost.
204. Plain and butt welds may be used on materials upto thickness of about
(a) 5 mm
(b) 10 mm
(c) 25 mm
(d) 40 mm
Answer : (c) 25 mm
205. In upset butt welding
(a) the faces of the metal pieces to be joined are prepared for even contact.
(b) heating is obtained by the contact resistance of metal pieces to be welded.
(c) the voltage required is 2-8 V and current required ranges from 50 A to several hundred amperes depending upon maÂterial and the area to be welded at a time.
(d) all of the above.
Answer : (d) all of the above.
206. In flash-butt welding
(a) no special preparation of the faces to be welded is necessary.
(b) clean and pure weld is obtained.
(c) power requirement is less.
(d) all of the above.
Answer : (d) all of the above.
207. Spot welding process basically depends on
(a) generation of heat.
(b) application of forging pressure.
(c) both (a) and (b).
(d) ohmic resistance.
Answer : (c) both (a) and (b).
208. In spot welding, composition and thickness of the base metal determines the
(a) holding time.
(b) amount of weld current.
(c) amount of squeeze pressure.
(d) all of the above.
Answer : (d) all of the above.
209. The tips of the electrodes, for spot welding are made of
(a) carbon.
(b) copper alloy or pure copper.
(c) mica.
(d) porcelain.
Answer : (b) copper alloy or pure copper.
210. The power factor of a spot welding machine is expected to be about
(a) 0.3 to 0.5 lagging.
(b) 0.8 to 0.85 lagging.
(c) 0.75 to 0.85 lending.
(d) unity.
Answer : (a) 0.3 to 0.5 lagging.
211. During spot welding, the current flows for
(a) fraction of a minute.
(b) fraction of a second to several seconds.
(c) few milliseconds.
(d) few microseconds.
Answer : (b) fraction of a second to several seconds.
212. Spot welding is employed for
(a) thin metal sheets (thickness being usually limited to 10-12 mm).
(b) castings only.
(c) thick sections.
(d) rough and irregular surfaces.
Answer : (a) thin metal sheets (thickness being usually limited to 10-12 mm).
213. Spot welding
(a) makes the weld air tight.
(b) makes the weld water tight.
(c) provides mechanical strength.
(d) all of the above.
Answer : (c) provides mechanical strength.
214. In spot welding
(a) it is desirable to clean the sheets thoroughly before welding.
(b) the work-pieces being welded are pressed together by meÂchanical pressure exerted through electrodes.
(c) current required is above 5,000 A and the voltage between the electrodes is usually less than 2 V (open-circuit voltage less than 12 V).
(c) all of the above.
Answer : (c) all of the above.
215. Projection welding can be considered as a mass production form of
(a) seam welding.
(b) spot welding.
(c) upset welding.
(d) flash welding.
Answer : (b) spot welding.
216. In comparison to spot welding, projection welding has the advantage(s) of
(a) simple welding process, more output and good finished apÂpearance.
(b) electrode life is increased owing to use of low current density and low pressure.
(c) it is easy to weld certain parts which cannot be welded by spot welding .
(d) all of the above.
Answer : (d) all of the above.
217. In seam welding
(a) the workpiece is fixed and disc electrodes move.
(b) the workpiece moves but rotating electrodes are fixed.
(c) the electrodes used are of disc or roller shape.
(d) either (a) or (b) and (c).
Answer : (d) either (a) or (b) and (c).
218. In case of seam welding, the flow of current through the electrode should be
(a) intermittent.
(b) continuous.
(c) either (a) or (b).
Answer : (a) intermittent.
219. In …….. welding it is essential that the surfaces to be welded are clean, dust and dirt free.
(a) butt
(b) spot
(c) seam
(d) both spot and seam
Answer : (c) seam
220. Seam welding is normally not recommended for
(a)Â aluminium alloys.
(b) stainless and coated steels.
(c) copper and high copper alloys.
(d) alloys of nickel and magnesium.
Answer : (c) copper and high copper alloys.
221. In percussion welding
(a) the process used depends on the arc effect for heating and not on the resistance.
(b) the action of process is so rapid that there is little heating effect in the material adjacent to the weld.
(c) the equipment used is quite expensive.
(d) all of the above.
Answer : (d) all of the above.
222. The basic electrical requirement in arc welding is that there should be
(a) high open-circuit voltage.
(b) no arc blow.
(c) dc power supply.
(d) coated electrodes.
Answer : (a) high open-circuit voltage.
223. In arc welding, the temperature of the arc produced is of the order of
(a) 1,000°C
(b) 3,500-4,000°C
(c) 5.000-7,500°C
(d) 7,500-10,000°C
Answer : (b) 3,500-4,000°C
224. The electric arc has
(a) linear resistance characteristic.
(b) positive resistance characteristic.
(c) negative resistance characteristic.
(d) highly inductive characteristic.
Answer : (c) negative resistance characteristic.
225. In an electric arc welding, the voltage required to strike dc arc is about
(a) 50-60 V
(b) 80-90 V
(c) 100-120 V
(d) 220 V
Answer : (a) 50-60 V
226. In an electric arc welding, the voltage required to strike ac arc is about
(a) 50-60 V
(b) 80-90 V
(c) 100-120 V
(d) 230 V
Answer : (b) 80-90 V
227. In an electric arc welding, the voltage required to maintain the arc will be
(a) 250-500 V
(b) 150-250 V
(c) 20-30 V
(d) below 10 V
Answer : (c) 20-30 V
228. For an electric arc welding the current range is usually
(a) 50-1,000 A
(b) 30-50 A
(c) 20-30 A
(d) below 20 A
Answer : (a) 50-1,000 A
229. Increased heat due to shorter arc is harmful owing to
(a) burn through.
(b) excessive porosity.
(c) undercutting of base material.
(d) all of the above.
Answer : (d) all of the above.
230. Arc blow results in
(a) non-uniform weld beads.
(b) shallow weld puddle giving rise to weak weld.
(c) splashing out of metal from weld puddle.
(d) all of the above defects.
Answer : (d) all of the above defects.
231. Arc blow effects occurring with dc welding machines can be reduced by
(a) shortening the arc column length.
(b) reducing the welding current or electrode size or rate of travel of the electrode.
(c) wrapping the welding electrode cable a few turns around the work.
(d) all of the above.
Answer : (d) all of the above.
232. In an electric welding, major personal hazards are
(a) weld spatter.
(b) flying sparks.
(c) harmful infrared and ultraviolet rays from the arc.
(d) all of the above.
Answer : (d) all of the above.
233. During electric arc welding as the thickness of the metal to be welded increases
(a) voltage is increased keeping current the same.
(b) current is increased keeping voltage unchanged.
(c) current and voltage, both are increased.
(d) current and voltage, both are reduced.
Answer : (b) current is increased keeping voltage unchanged.
234. In a dc arc welding
(a) both electrode as well as workpiece are made + ve.
(b) both electrode as well as workpiece are made – ve.
(c) electrode is made -ve and workpiece + ve.
(d) electrode is made +ve and workpiece – ve.
Answer : (c) electrode is made -ve and workpiece + ve.
235. The length of are required depends on
(a) kind of electrodes used, its coating and its diameter.
(b) magnitude of current used.
(c) position of welding.
(d) all of the above.
Answer : (d) all of the above.
236. Overhead welding position is thought to be the most
(a) hazardous.
(b) economical.
(c) useful.
(d) difficult.
Answer : (a) hazardous.
237. In arc welding best results are obtained when arc length is equal to
(a) 25 mm.
(b) 19 mm.
(c) diameter of electrode.
(d) double the diameter of the electrode.
Answer : (c) diameter of electrode.
238. Flat position welding is considered to be the most
(a) easiest and economical.
(b) hazardous.
(c) adaptable for welding of both ferrous and non-ferrous metals particularly for cast iron.
(d) both (a) and (c).
Answer : (d) both (a) and (c).
239. In direct current straight polarity (DCSP) or electrode negative welding
(a) heavily coated electrodes are used.
(b) base metal penetration is narrow and deep.
(c) electrode is the hottest.
(d) workpiece is relatively cooler.
Answer : (b) base metal penetration is narrow and deep.
240. In direct current reverse polarity or electrode positive welding
(a) workpiece is the hottest.
(b) bare and medium coated electrodes can be used.
(c) electrode is the hottest.
(d) base metal penetration is narrow and deep.
Answer : (c) electrode is the hottest.
241. The electrode is coated in order to
(a) improve bead quality.
(b) cleanse the base metal.
(c) provide shielding to weld pool.
(d) prevent atmospheric contamination.
Answer : (a) improve bead quality.
242. In DCRP or electrode positive welding, the heat produced at the electrode is ………. of total heat produced.
(a) one-third.
(b) two-third.
(c) three-fourth.
(d) one-fourth.
Answer : (b) two-third.
243. A 10 SWG electrode usually operates in the current range of
(a) 95-135 A
(b) 80-95 A
(c) 45-70 A
(d) 20-30 A
Answer : (a) 95-135 A
244. Electrode of 8 SWG is to be employed for welding two 12.5 mm steel plates. The current required will of the order of
(a) 20 A
(b) 50 A
(c) 150 A
(d) 250 A
Answer : (c) 150 A
245. The purpose of coating on arc welding electrodes is to
(a) provide a protective covering.
(b) provide slag for protection of the molten metal.
(c) stabilize the arc.
(d) all of the above.
Answer : (d) all of the above.
246. 20 per cent duty cycle of a welding machine means
(a) operation of machine for 2 minutes in a duration of 10 minutes.
(b) machine output is 20 per cent of rated output.
(c) machine operates at 20 per cent efficiency.
(d) operation of machine is for 1 minute in a duration of 5 minutes.
Answer : (a) operation of machine for 2 minutes in a duration of 10 minutes.
247. In carbon arc welding, if the electrode is connected to the + ve terminal of the dc supply
(a) arc will not strike.
(b) arc will be dull.
(c) carbon arc will have tendency to go in to the weld joint.
(d) metal will not melt.
Answer : (c) carbon arc will have tendency to go in to the weld joint.
248. Carbon arc welding has the main drawback of
(a) occurrence of blow holes owing to magnetic arc blow espeÂcially while welding near edges of the workpiece.
(b) need of separate filler.
(c) necessity of bare electrodes.
(d) fast consumption of electrodes.
Answer : (a) occurrence of blow holes owing to magnetic arc blow espeÂcially while welding near edges of the workpiece.
249. Carbon arc welding
(a) uses carbon or graphite rod as a negative electrode and work to be welded as a positive.
(b) cannot be done with ac supply.
(c) is not suitable for vertical and overhead welding.
(d) all of the above.
Answer : (d) all of the above.
250. Carbon arc welding is suitable particularly for …….. metals.
(a) ferrous.
(b) nonferrous.
(c) all.
Answer : (b) nonferrous.
251. For metal arc welding
(a) both dc and ac can be used but ac is preferred.
(b) bare electrodes are no longer used except for automatic weldÂing having arrangement to protect the weld area from the atmosphere.
(c) correct welding current, voltage and speed are very imporÂtant.
(d) all of the above.
Answer : (d) all of the above.