All Free Electrical Engineering MCQs with Answers

• A. Ward Leonard control
• B. rheostatic control
• C. any of the above method
• D. none of the above method

Explanation: Ward-Leonard control varies the armature voltage using a motor-generator set, allowing speed reduction with little energy wastage compared…

• A. run at normal speed
• B. not run
• C. run at lower speed
• D. burn due to heat produced in the field winding by .eddy currents

Explanation: An ordinary DC shunt motor on AC has a highly inductive field and armature reaction, producing poor torque and excessive losses, including…

• A. shunt motor
• B. series motor
• C. differential compoutid D.C. motor
• D. cumulative compound D.C. motor

Explanation: Shears and punches need a high starting and overload torque, which is supplied by a cumulative compound motor through the series-field…

• A. it limits the speed of the motor
• B. it limits the starting current to a safe value
• C. it starts the motor
• D. none of the above

Explanation: At starting, the motor back emf is zero, so the armature would draw an excessive current limited only by its very low resistance.

• A. has its field winding consisting of thick wire and less turns
• B. has a poor torque
• C. can be started easily without load
• D. has almost constant speed

Explanation: The series field carries the full armature current and therefore uses thick wire with relatively few turns to keep its resistance low.

• A. the speed will increase abruptly
• B. the speed will increase in proportion to reduction in load
• C. the speed will remain almost/constant
• D. the speed will reduce

Explanation: A shunt motor has nearly constant field flux, and its speed automatically changes only slightly as load varies.

• A. these motors have high starting torque
• B. these motors are not self-starting
• C. back e.m.f. of these motors is zero initially
• D. to restrict armature current as there is no back e.m.f. while starting

Explanation: At starting, the motor has zero back e.m.f., so the armature would draw an excessive current limited only by its very low resistance.

• A. the speed of motor will be reduced %
• B. the armature current will reduce
• C. the motor will attain dangerously high speed 1
• D. the motor will continue to nuvat constant speed

Explanation: Opening the shunt field greatly reduces flux, and motor speed varies approximately inversely with flux for a given back e.m.f.

• A. current in the conductor aovtaat of conductor
• B. resultant force on conductor
• C. none of the above

Explanation: Fleming’s left-hand rule assigns the forefinger to magnetic field, the middle finger to current, and the thumb to force or motion.

• A. Shunt motor
• B. Series motor
• C. Differential compound motor
• D. Cumulative compound motor

Explanation: Elevators require high starting torque and reasonably controlled speed, which is provided by the series-field torque of a cumulative…

• A. high starting torque
• B. low starting torque
• C. variable speed
• D. frequent on-off cycles

Explanation: In a differential compound motor, the series field opposes the shunt field, reducing the net flux as load increases and giving…

• A. Series motor
• B. Shunt motor
• C. Cumulative compound motor
• D. Differential compound motor

Explanation: Machine tools generally need nearly constant speed despite load changes, which is the main characteristic of a shunt motor.

• A. Lathe machine
• B. Centrifugal pump
• C. Locomotive
• D. Air blower

Explanation: A locomotive must start by moving a heavy train, so it requires very high starting torque.

• A. interchanging supply terminals
• B. interchanging field terminals
• C. either of A. and B. above
• D. None of the above

Explanation: Reversing only the field connections reverses the field relative to the armature current and hence reverses torque.

• A. Shunt motor
• B. Series motor
• C. Cumulative compound motor
• D. Differentiate compound motor

Explanation: A series motor has very high no-load speed because its flux becomes small when armature current and series-field current are small.

• A. the pressure in the turbine rotor is approximately same as in con¬denser
• B. the pressure in the turbine rotor is higher than pressure in the con¬denser
• C. the pressure in the turbine rotor gradually decreases from inlet to exit from condenser
• D. none from the above

Explanation: A De Laval turbine is an impulse turbine, so nearly the entire pressure drop occurs in the nozzle and the rotor pressure remains almost…

• A. is same
• B. is different
• C. increases from one side to the other side
• D. decreases from one side to the other side

Explanation: In an impulse wheel, the moving blades only change the velocity and direction of steam; ideally, they produce no pressure drop.

• A. there is enthalpy drop in fixed and moving blades
• B. there is enthalpy drop only in moving blades
• C. there is enthalpy drop in nozzles
• D. none of the above

Explanation: For an impulse turbine, the pressure and enthalpy drop occur in the fixed nozzles, which convert enthalpy into steam velocity.

• A. increase in dryness fraction of exit steam
• B. decrease in dryness fraction of exit steam
• C. no change in the quality of exit steam
• D. decrease or increase of dryness fraction of exit steam depending upon inlet quality

Explanation: Nozzle friction increases the actual exit enthalpy at the same pressure, and for wet steam this corresponds to a higher dryness fraction.

• A. increase in exit velocity from the nozzle
• B. decrease in exit velocity from the nozzle
• C. no change in exit velocity from the nozzle
• D. increase or decrease depending upon the exit quality of steam

Explanation: Friction dissipates part of the available enthalpy drop inside the nozzle, leaving less energy for conversion into kinetic energy.