Question

The diagram shows two magnets and two iron rods placed in a line. Which magnetic poles are induced at the ends J and K of the iron rods?

(A) Pole induced at end J – N, pole induced at end K – N.
(B) Pole induced at end J – N, pole induced at end K – S.
(C) Pole induced at end J – S, pole induced at end K – N.
(D) Pole induced at end J – S, pole induced at end K – S.

Answer 1

Hint: A magnet is always a dipole. So when an iron rod is kept close to a magnet, the pole induced on an end of the iron rod depends on the pole of the magnet that it is closest to. The pole opposite to that of the magnet’s pole it is closest to is induced at the end of the rod.

Complete step by step answer:
From the figure, we can see that there are two rods and two magnets kept alternatively. The north pole of both the magnets is to the left and their south pole is to the right.
Now for the first rod, point J is closest to the south pole of the first magnet and the other end of the iron rod is closest to the north pole of the second magnet. The magnetic pole that is induced on one of the ends of the iron rod will be the opposite to the pole of the magnet that it is closest to.
So the point J of the first iron rod is closest to the south pole of the first magnet and hence there will be a north pole induced in it and the opposite end will have a south pole, being close to a north pole.
For the second iron rod, one end of the rod is close to the south pole of the second magnet and hence at that point, a north pole will be induced. And since magnets are always dipole, so the opposite end of the iron rod that is the point K will have a south pole induced.
Therefore, the pole induced at end J is north and the pole induced at the end K is south.
So the correct answer is option (B).

Note:
The feature of some substances that can have magnetic poles induced in them temporarily or permanently can have huge applications. Electromagnetic induction can be used to power a huge number of electrical devices and one of the most common examples being the electrical generators.