All Free Electrical Engineering MCQs with Answers

• A. case iron
• B. carbon
• C. silicon steel
• D. stainless steel

Explanation: Armature-core laminations are made from silicon steel because its high electrical resistivity reduces eddy-current loss and its magnetic…

• A. copper lugs
• B. resistance wires
• C. insulation pads
• D. brazing

Explanation: Commutator segments are joined to the armature coil ends using copper lugs, which provide a strong, low-resistance electrical connection.

• A. length of conductor
• B. cross-sectional area of the conductor
• C. number of conductors
• D. all of the above

Explanation: From R = ρL/A, resistance increases with conductor length and decreases with cross-sectional area; the number of conductors affects the…

• A. mica
• B. copper
• C. cast iron
• D. carbon

Explanation: Field coils carry current and must produce the required magnetic field with low resistance, so they are normally wound from insulated…

• A. copper is harder than mica
• B. mica and copper are equally hard
• C. mica is harder than copper
• D. none of the above

Explanation: Mica is harder than copper, so it is used as insulation between commutator segments and must be undercut slightly below the copper surface…

• A. motion of conductor
• B. lines of force
• C. either of the above
• D. none of the above

Explanation: In Fleming’s right-hand rule, the thumb shows conductor motion, the forefinger shows magnetic-field or flux direction, and the middle…

• A. direction of induced e.m.f.
• B. direction of flux
• C. direction of motion of the conductor if forefinger points in the direction of generated e.m.f.
• D. direction of motion of conductor, if forefinger points along the lines of flux

Explanation: With the forefinger along the flux lines, Fleming’s right-hand rule places the thumb in the direction of conductor motion and the middle…

• A. rivets
• B. counter sunk screws
• C. brazing
• D. welding

Explanation: Pole shoes are normally secured to the pole cores with countersunk screws, which provide a firm mechanical connection while keeping the…

• A. magnetic flux, direction of current flow and resultant force
• B. magnetic flux, direction of motion and the direction of e.m.f. induced
• C. magnetic field strength, induced voltage and current
• D. magnetic flux, direction of force and direction of motion of conductor

Explanation: Fleming’s right-hand rule relates the magnetic-flux direction, the motion of the conductor, and the direction of induced e.m.f.

• A. current
• B. voltage
• C. speed
• D. none of above

Explanation: Mechanical losses consist mainly of friction and windage, both of which increase with rotational speed.

• A. where low voltage and high currents are involved
• B. where high voltage and small cur-rents are involved
• C. in both of the above cases
• D. in none of the above cases

Explanation: Copper brushes have low contact resistance and are therefore suitable for low-voltage, high-current operation.

• A. Lap winding
• B. Wave winding
• C. Either of A. and B. above
• D. Depends on other features of design

Explanation: Generated e.m.f. is inversely related to the number of parallel paths. Wave winding normally has only two parallel paths, whereas lap…

• A. severe sparking
• B. rough commutator surface
• C. imperfect contact
• D. any of the above

Explanation: Severe sparking, a rough commutator surface, and imperfect brush contact can all damage the brush surface and increase wear.

• A. ball bearings
• B. bush bearings
• C. magnetic bearmgs
• D. needle bearings

Explanation: Ball bearings are commonly used to support the rotor shaft in smaller and general-purpose DC machines because they provide low friction…

• A. double the number of poles
• B. same as the number of poles
• C. half the number of poles
• D. two

Explanation: In a simplex lap winding, the number of parallel paths is equal to the number of poles, so one brush is normally provided for each pole.

• A. all the four poles are north poles
• B. alternate poles are north and south
• C. all the four poles are south poles
• D. two north poles follow two south poles

Explanation: Adjacent poles in a DC machine must have opposite polarities so that the armature conductors experience alternating magnetic fields.

• A. is amenable to better voltage control
• B. is more stable
• C. has exciting current independent of load current
• D. has all above features

Explanation: A separately excited generator has an independent field supply, allowing better voltage control and making its field current independent…

• A. field control method
• B. armature controlled method
• C. field diverter
• D. frequency control method

Explanation: The Ward Leonard system varies the DC motor armature voltage by supplying it from a separately driven generator, while the field is…

• A. decrease in speed
• B. increase in speed
• C. short circuit
• D. open circuit

Explanation: Armature reaction weakens and distorts the main flux in a DC motor. For a given back EMF requirement, the weakened flux causes the motor…

• A. series with field winding
• B. series speed armature winding
• C. parallel big field winding
• D. parallel with armature winding

Explanation: Interpoles must produce a magnetic field proportional to armature current so they can counteract armature reaction during commutation.