[amp_mcq option1=”All the four poles are north poles” option2=”Alternate poles are north and south” option3=”machine A. All the four poles are north poles B. Alternate poles are north and south C. All the four poles are south poles” option4=”Two north poles follow two south poles” correct=”option2″]
The correct answer is: B. Alternate poles are north and south.
A four-pole D.C. machine has two pairs of poles, with each pair consisting of a north pole and a south pole. The poles are arranged so that the north pole of one pair is next to the south pole of the other pair. This arrangement creates a magnetic field that rotates the armature of the machine.
Option A is incorrect because it states that all four poles are north poles. This would create a magnetic field that is not strong enough to rotate the armature.
Option C is incorrect because it states that all four poles are south poles. This would also create a magnetic field that is not strong enough to rotate the armature.
Option D is incorrect because it states that two north poles follow two south poles. This would create a magnetic field that is not continuous, and would therefore not be able to rotate the armature.