Animated Solution for Physics - Magnetic Effects of Current: Needles $N_1,N_2$ and $N_3$ are made of a ferromagnetic, a paramagnetic and a diamagnetic substance respectively. A magnet when brought close to them will

Imagine you are holding a powerful bar magnet, and on the table in front of you lie three mysterious needles: $N_1$, $N_2$, and $N_3$. They look identical, but they harbor entirely different "magnetic personalities." The first is ferromagnetic, the second is paramagnetic, and the third is diamagnetic.

Our mission is to deduce exactly how each needle will react when the magnet is brought close. To do this, we must dive into the atomic realm and understand how their internal electrons respond to an external magnetic field.

The Enthusiastic Follower

Let's start with $N_1$, the ferromagnetic needle. Materials like iron, nickel, and cobalt fall into this category. Inside a ferromagnetic material, atoms group together into microscopic regions called domains.

When an external magnetic field is applied, these domains enthusiastically snap into alignment with the field. This creates a massive induced magnetic moment in the same direction as the applied field. Because the induced poles are opposite to the magnet's poles (e.g., the magnet's North pole induces a South pole on the near end of the needle), the result is a strong attractive force. The magnet will pull $N_1$ violently towards it.

The Lazy Supporter

Next is $N_2$, the paramagnetic needle. Think of materials like aluminum or platinum. These materials possess unpaired electrons, giving individual atoms a permanent magnetic dipole moment.

However, unlike ferromagnets, they lack the strong domain structure. When the external magnet approaches, the atomic dipoles try to align with the field, but random thermal agitation constantly knocks them out of place. As a result, they only manage a weak alignment in the direction of the field. This translates to a weak attractive force. The magnet will pull $N_2$, but very gently.

The Stubborn Rebel

Finally, we arrive at $N_3$, the diamagnetic needle. Materials like copper, bismuth, and water are diamagnetic. These are the true rebels of the magnetic world.

Diamagnetism arises from the orbital motion of electrons. According to Lenz's Law at the atomic scale, when an external magnetic field is applied, the electron orbits shift slightly to create an induced magnetic field that opposes the change. This means the needle develops a weak magnetic moment in the exact opposite direction of the applied field. Because like poles repel, the magnet will exert a weak repulsive force on $N_3$, pushing it away.

By combining our atomic insights, the macroscopic behavior becomes crystal clear. The magnet will attract $N_1$ strongly, attract $N_2$ weakly, and repel $N_3$ weakly. This perfectly matches option (b), giving us our final answer.

Always remember: Ferromagnets love magnets, paramagnets like them a little, and diamagnets want nothing to do with them!