By Surendra | June 10, 2020 0 Comment 0% 3 Created by Surendra DC Motors Quiz in English Set 1 All Important Question Answers for Electrician Related Exams 1 / 25 What will happen if the back e.m.f. of a D.C. motor vanishes suddenly? The motor will stop The motor will run noisy The armature may burn The motor will continue to run 2 / 25 Which of the following motor is preferred for operation in highly explosive atmosphere ? Battery operated motor Shunt motor Series motor Air motor 3 / 25 If a D.C. motor is connected across the A.C. supply it will run at lower speed run at normal speed not run burn due to heat produced in the field winding by .eddy currents 4 / 25 A three point starter is considered suitable for shunt motors shunt as well as compound motors shunt compound and series motors all D.C. motors 5 / 25 can be obtained by increasing the armature current decreasing the armature current decreasing the field current increasing the field current 6 / 25 Sparking is discouraged in a D.C. motor because commutator gets damaged both and it increases the input power con-sumption none of the above 7 / 25 If the speed of a D.C. shunt motor is increased the back e.m.f. of the motor will remain same increase become zero decrease 8 / 25 Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ? Coloumb’s law Faraday’s law Lenz’s law Fleming’s left-hand rule 9 / 25 In which of the following applications D.C. series motor is invariably tried? Fan motor Motor operation in A.C. or D.C. Drive for a water pump Starter for a car 10 / 25 When two D.C. series motors are connected in parallel the resultant speed is more than the normal speed loss than the normal speed normal speed zero 11 / 25 A D.C. series motor is that which has a poor torque has almost constant speed can be started easily without load has its field winding consisting of thick wire and less turns 12 / 25 In case the back e.m.f. and the speed of a D.C. motor are doubled the torque developed by the motor will be doubled increase four folds reduce to one-fourth value remain unchanged 13 / 25 The ratio of starting torque to full-load torque is least in case of none of the above series motors shunt motors compound motors 14 / 25 Sparking at the commutator of a D.C. motor may result in damage to commutator insulation damage to commutator segments all of the above increased power consumption 15 / 25 In case of D.C. shunt motors the speed is dependent on back e.m.f. only because flux is proportional to armature current flux is practically constant in D:C. shunt motors back e.m.f. is equal to armature drop armature drop is negligible 16 / 25 In a D.C. shunt motor speed is proportional to the square of the current independent of armature current inversely proportional to the armature current directly proportional to the armature current 17 / 25 Usually wide and sensitive speed control is desired in case of elevators steel rolling mills colliery winders centrifugal pumps 18 / 25 Which of the following method of speed control of D.C. machine will offer minimum efficiency ? Armature control method Voltage control method All above methods Field control method 19 / 25 A direct on line starter is used: for starting motors up to 20 H.P. up to 5 H.P. up to 10 H.P. up to 15 H.P. 20 / 25 Three point starter can be used for shunt motor only compound motor only series motor only both shunt and compound motor 21 / 25 These days D.C. motors are widely used in air compressors machine shops pumping sets electric traction 22 / 25 In D.C. machines fractional pitch winding is used to reduce copper losses to increase the generated e.m.f. to reduce the sparking to improve cooling 23 / 25 Speed control by Ward Leonard method gives uniform speed variation below normal speed only in one direction in both directions above normal speed only. 24 / 25 Which of the following motors one will choose to drive the rotary compressor ? Universal motor Synchronous motor D.C. series motor D.C. shunt motor 25 / 25 Starters are used with D.C. motors because these motors are not self-starting back e.m.f. of these motors is zero initially to restrict armature current as there is no back e.m.f. while starting these motors have high starting torque कृपया सही सूचना भरें ताकि सर्टिफिकेट ईमेल पर भेजा जा सकें। NameEmailPhone NumberDistrictSchool/Coaching Name Your score is LinkedIn Facebook VKontakte 0% Restart quiz आपको यह क्विज अच्छी लगी तो 5 स्टार रेटिंग जरुर दें । Send feedback
