Important MCQ Question Of DC Generator | Objective Type Question Of DC Generator

Explanation:

• Brush wear can occur due to many reasons such as server sparking, excessive heat, Imperfect contacts etc.
• Therefore Brushes required periodic maintenance.

Explanation: As we know that 

• E.M.F equation of d.c generator is
  
  
• Now for Lap wound generator  A = P
  Where is A = Number of parallel path
  And P = Number of poles
• Therefor in Lap wound D.C generator they canceled each other.
• For Wave wound Generator A = 2
• Therefore the E.M.F is greater in Wave wound D.C generator than Lap wound.

Explanation:

• The area swept by conductor in 1 second = lv
• The flux cut by conductor in 1 second = Blv
• Then the emf induced in a straight conductor of length l moving with velocity v perpendicular to a magnetic field B is
  E = Blv
• Where B,l, and v are mutually perpendicular to each other.

Explanation:

• Since the winding is two layer winding therefore, the total number of conductor  16 × 2 = 32.
• Pole pitch of a DC generator is the ratio of the total number of the conductor to the number of poles.
• Pole pitch = Number of conductor / Number of poles = 32 / 4 = 8
• Therefore number of pole pitch = 8.

Explanation:

• Eddy current losses can be reduced by using laminated core.
• But Hysteresis losses can not be reduced in this way.
• For reducing hysteresis loss those metal are chosen for armature core which has low hysteresis coefficient.
• Therefore silicon steel such as stalloys is used for armature core.
• This stalloys not only have low hysteresis coefficient but also possess high electric resistivity.

Explanation:

• According to Faraday’s law of electromagnetic induction rotating armature cuts the magnetic field, due to which an emf is induced in it.
• This emf generate the eddy current which causes eddy current loss.
• Therefore to reduce the effect of eddy current the armature core is laminated.
• The thickness of lamination is between 0.1 to 0.5 mm. 

Explanation:

• There are four factors that influence the resistance in a conductor.
  ⇒Thickness (cross sectional area of the wire). (R ∝ 1/A)
  ⇒Length ( R ∝ L)
  ⇒Temperature
  ⇒Conductivity of material
• The number of armature conductor “Z” is constant that depends upon the number of turns on the armature and the type of winding. i.e wave winding or lap winding.

Explanation:

• Fleming’s right-hand rule (for generators) shows the direction of induced current when a conductor attached to a circuit moves in a magnetic field.
• It can be used to determine the direction of current in a generator’s windings.
  
  

• The right hand is held with the thumb, first finger and second finger mutually perpendicular to each other (at right angles), as shown in the diagram.
• The thumb is pointed in the direction of the motion of the conductor relative to the magnetic field.
• The forefinger finger is pointed in the direction of the magnetic field. (north to south)
• Then the middle finger represents the direction of the induced or generated current.

Explanation:

• Mica is used as the insulating material for the commutator segments.
• Due to its mechanical strength and insulating properties, mica is a very satisfactory material.
• Mica is a good electrical insulator (bad conductor of electricity) at the same time as being a good thermal conductor.
• Mica is much harder than copper.
• In Mohs scale for finding hardness from scale 1 to 10 where 1 is the hardest metal.
• Mica hardness is 2.5.
• Whereas hardness of copper is 3.

Explanation:

• The thumb is pointed in the direction of the motion of the conductor relative to the magnetic field.
• For more information check Que no:18.