Problem 1979 - JEE Physics

Question

Needles \(\mathrm{N}_{1}, \mathrm{~N}_{2}\) and \(\mathrm{N}_{3}\) are made of a ferromagnetic, a paramagnetic and a diamagnetic substance respectively. A magnet when brought close to them will (a) Attract \(\mathrm{N}_{1}\) strongly, \(\mathrm{N}_{2}\) weakly and repel \(\mathrm{N}_{3}\) weakly (b) Attract \(\mathrm{N}_{1}\) strongly, but repel \(\mathrm{N}_{2}\) and \(\mathrm{N}_{3}\) weakly (c) Attract all three of them (d) Attract \(\mathrm{N}_{1}\) and \(\mathrm{N}_{2}\) strongly but repel \(\mathrm{N}_{2}\)

Step-by-Step Solution

Answer

The correct answer is (a) Attract \(N_{1}\) strongly, \(N_{2}\) weakly, and repel \(N_{3}\) weakly.

Step 1: Considering the properties of ferromagnetic materials

A ferromagnetic material has a strong magnetic moment and gets attracted to a magnetic field. When a magnet is brought close to a ferromagnetic material, it will be attracted strongly.

Step 2: Considering the properties of paramagnetic materials

A paramagnetic material has a weak magnetic moment and gets attracted to a magnetic field but to a smaller extent compared to ferromagnetic materials. When a magnet is brought close to a paramagnetic material, it will be attracted weakly.

Step 3: Considering the properties of diamagnetic materials

A diamagnetic material has no inherent magnetic moment and gets weakly repelled by a magnetic field. When a magnet is brought close to a diamagnetic material, it will be repelled weakly.

Step 4: Matching the results with the given options

According to our analysis: - N1, which is made of a ferromagnetic substance, will be attracted strongly - N2, which is made of a paramagnetic substance, will be attracted weakly - N3, which is made of a diamagnetic substance, will be repelled weakly Comparing these findings with the given options, we can conclude that the correct answer is (a) Attract N1 strongly, N2 weakly, and repel N3 weakly.

Key Concepts

Ferromagnetic Materials

Ferromagnetic materials are among the most magnetic of all materials, standing out due to their strong attraction to magnets. Common examples include iron, nickel, and cobalt. These materials can become magnetized themselves when exposed to a magnetic field. This is because they have numerous unpaired electrons whose magnetic moments align in the same direction.
This alignment leads to a strong magnetic moment packed in these materials, meaning they will be strongly attracted to external magnets. In practical uses, ferromagnetic materials are vital for making permanent magnets and are used in various applications like electric motors, transformers, and hard drives.

• Strong magnetic attraction.
• Alignment of magnetic moments.
• Used in various electrical applications.

Paramagnetic Materials

Paramagnetic materials, on the other hand, have a weaker response to magnetic fields compared to ferromagnetic materials. Substances like aluminum and platinum fall into this category. They contain unpaired electrons, but the magnetic moments do not align as strongly or consistently as in ferromagnetic materials.
When a magnet is brought near paramagnetic materials, they exhibit a weak attraction, which is often noticeable only under sensitive instruments. Unlike ferromagnetic materials, they do not retain magnetization after the external magnetic field is removed since their magnetic domains are not aligned permanently.

• Weak magnetic attraction.
• Temporary magnetization.
• Examples include aluminum and platinum.

Diamagnetic Materials

Diamagnetic materials have a very different interaction with magnetic fields. These materials create an induced magnetic field in the opposite direction when exposed to an external magnetic field, leading to a weak repulsion. Most materials have diamagnetic properties, but they are usually overshadowed by stronger magnetic behaviors in paramagnetic and ferromagnetic materials.
Examples include copper, gold, and bismuth. In diamagnetic materials, paired electrons cancel each other's magnetic fields, resulting in zero net magnetic moment. Therefore, when these materials come close to a magnet, they experience a weak repulsive force.

• Weak magnetic repulsion.
• No net magnetic moment (paired electrons).
• Commonly found in materials like copper and gold.