All Free Electrical Engineering MCQs with Answers

• A. not develop starting torque
• B. fail to start without load
• C. run at dangerously high speed
• D. draw more current without producing sufficient torque

Explanation: For a DC series motor, flux decreases sharply when the load is removed, while torque is not needed to sustain rotation.

• A. voltage control method
• B. flux control method
• C. rheostat control method
• D. all of the above

Explanation: A DC shunt motor can be controlled by varying armature voltage, varying field flux, or inserting resistance in the armature circuit.

• A. If the field winding resistance of a DC shunt motor is increases, its speed will
• B. decreases
• C. increases
• D. remains same
• E. none of the above

Explanation: Increasing the shunt-field resistance reduces field current and therefore weakens the flux.

• A. decreases
• B. increases
• C. remain same
• D. none of the above

Explanation: A temperature rise increases the resistance of the series field and armature windings, causing a larger internal voltage drop and…

• A. decreases.
• B. increases
• C. remain same
• D. none of the above

Explanation: Heating increases the shunt-field winding resistance, so field current and flux decrease.

• A. dc generator
• B. dc motor
• C. transformer
• D. all of the above

Explanation: In a DC motor, the generated back emf opposes the applied voltage and armature current, which is why it is called back emf.

• A. increase in armature current
• B. increase in flux
• C. decrease in reactance
• D. decrease in back emf

Explanation: An increased load raises armature current, increasing the armature resistance drop.

• A. runs as a generator
• B. does not run as a generator
• C. also runs as a motor comes to stop after sometime

Explanation: When the second DC motor is excited and mechanically driven by the first motor, its armature conductors cut magnetic flux and generate…

• A. reducing the field current
• B. decreasing the armature current
• C. increasing the armature current
• D. increasing the excitation current
• E. none of the above methods

Explanation: Speed of a shunt motor can be increased above its normal value by field weakening.

• A. the field
• B. the armature
• C. the brushes
• D. the commutator

Explanation: Iron losses are caused by alternating magnetisation of the iron core, producing hysteresis and eddy-current losses.

• A. Series motor
• B. Shunt motor
• C. Cumulatively compounded motor
• D. Differentially compounded motor

Explanation: A series motor has the strongest automatic speed response to load changes: increased load current strengthens its flux and reduces speed…

• A. series motor
• B. shunt motor
• C. compound motor
• D. any of the above

Explanation: A compound motor is suitable for a load that varies from nearly zero to a short-duration peak because it combines good no-load speed…

• A. series motor
• B. shunt motor
• C. compound motor
• D. any of the above

Explanation: A series motor is suitable when the load remains present but periodically reaches a high peak, because its series field provides high…

• A. drum type controller is used
• B. three point starter is used
• C. four point starter is used
• D. all above can be used

Explanation: A drum controller is designed for frequent starting, stopping, reversing and speed control of comparatively large motors.

• A. self-induced e.m.f.
• B. mutually induced e.m.f.
• C. back e.m.f
• D. none of the above

Explanation: As a motor armature rotates, it cuts the magnetic flux and generates an e.m.f. opposing the applied voltage, so it is called back e.m.f.

• A. a stronger commutating field is needed at low speed than at high speed
• B. a weaker commutating field is needed at low speed than at high speed
• C. same commutating field is needed at low speed than at high speed
• D. none of the above is correct

Explanation: At higher speed, commutation occurs in less time, so a stronger interpole or commutating field is needed to reverse armature current…

• A. Plugging
• B. Regenerative braking
• C. Rheostatic braking
• D. None of the above

Explanation: Plugging applies a reverse torque and brings an elevator to rest quickly, which is important for accurate stopping at floors.

• A. Shunt motors
• B. Series motors
• C. Compound motors
• D. All of the above

Explanation: Dynamic braking converts the motor into a generator and dissipates the generated energy in a resistance.

• A. motor is run as a generator
• B. motor is reversed in direction
• C. motor is run at reduced speed

Explanation: In rheostatic or dynamic braking, the supply is disconnected and the running motor is connected as a generator feeding a braking resistor.

• A. no-load
• B. part load
• C. full-load
• D. overload

Explanation: Hopkinson’s test is a regenerative back-to-back test in which one machine operates as a motor and the other as a generator, normally at…