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 Speed control by Ward Leonard method gives uniform speed variation below normal speed only in one direction in both directions above normal speed only. 2 / 25 Starters are used with D.C. motors because to restrict armature current as there is no back e.m.f. while starting these motors have high starting torque back e.m.f. of these motors is zero initially these motors are not self-starting 3 / 25 These days D.C. motors are widely used in pumping sets electric traction air compressors machine shops 4 / 25 When two D.C. series motors are connected in parallel the resultant speed is zero normal speed more than the normal speed loss than the normal speed 5 / 25 Usually wide and sensitive speed control is desired in case of colliery winders elevators centrifugal pumps steel rolling mills 6 / 25 In case of D.C. shunt motors the speed is dependent on back e.m.f. only because back e.m.f. is equal to armature drop flux is proportional to armature current flux is practically constant in D:C. shunt motors armature drop is negligible 7 / 25 can be obtained by increasing the field current decreasing the field current increasing the armature current decreasing the armature current 8 / 25 A three point starter is considered suitable for all D.C. motors shunt compound and series motors shunt motors shunt as well as compound motors 9 / 25 Sparking at the commutator of a D.C. motor may result in all of the above damage to commutator insulation damage to commutator segments increased power consumption 10 / 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 11 / 25 The ratio of starting torque to full-load torque is least in case of compound motors none of the above shunt motors series motors 12 / 25 In which of the following applications D.C. series motor is invariably tried? Drive for a water pump Motor operation in A.C. or D.C. Starter for a car Fan motor 13 / 25 Which of the following motors one will choose to drive the rotary compressor ? D.C. series motor Synchronous motor D.C. shunt motor Universal motor 14 / 25 Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ? Faraday’s law Fleming’s left-hand rule Coloumb’s law Lenz’s law 15 / 25 Which of the following motor is preferred for operation in highly explosive atmosphere ? Battery operated motor Series motor Air motor Shunt motor 16 / 25 If the speed of a D.C. shunt motor is increased the back e.m.f. of the motor will become zero remain same increase decrease 17 / 25 Three point starter can be used for shunt motor only series motor only both shunt and compound motor compound motor only 18 / 25 In a D.C. shunt motor speed is proportional to the square of the current inversely proportional to the armature current directly proportional to the armature current independent of armature current 19 / 25 A direct on line starter is used: for starting motors up to 20 H.P. up to 10 H.P. up to 15 H.P. up to 5 H.P. 20 / 25 What will happen if the back e.m.f. of a D.C. motor vanishes suddenly? The armature may burn The motor will run noisy The motor will continue to run The motor will stop 21 / 25 Sparking is discouraged in a D.C. motor because it increases the input power con-sumption commutator gets damaged none of the above both and 22 / 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 increase four folds reduce to one-fourth value remain unchanged be doubled 23 / 25 If a D.C. motor is connected across the A.C. supply it will burn due to heat produced in the field winding by .eddy currents not run run at lower speed run at normal speed 24 / 25 Which of the following method of speed control of D.C. machine will offer minimum efficiency ? Armature control method All above methods Field control method Voltage control method 25 / 25 In D.C. machines fractional pitch winding is used to improve cooling to reduce the sparking to increase the generated e.m.f. to reduce copper losses 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
