Which of the following correctly represents the sequence of operations of isolator, circiut breaker and earthing switch while opening a circuit?

Two parallel conductors are carrying the current in the same direction. Which of the following statements is correct?

The purpose of interpoles in DC machines is to nullify

interpoles is widely use to improve commutation
place between main poles fitted to yoke
functions:
to neutralize armature mmf in commutating zone
to produce some flux in commutating zone

A fuse is inserted in

Due to skin effect

Skin Effect:
tendency of the current to crowd near the conductor surface.

Skin effect is proportional to frequency, conductor diameter and permiability.
Skin effect increases effective resistance of conductor.
In DC, no skin effect.

The form factor in AC means the ration of