Question

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:

• A. attract $N_1$ and $N_2$ strongly but repel $N_3$
• B. attract $N_1$ strongly, $N_2$ weakly and repel $N_3$ weakly
• C. attract $N_1$ strongly, but repel $N_2$ and $N_3$ weakly
• D. attract all three of them

Answer 1

Answer: (B)

Ferromagnetic subsiances have strong tendency to get magnetised (induced magnetic moment) in the same direction as that of applied magnetic field, so magnet attracts $N_1$ strongly. Paramagnetic substances get weakly magnetised (magnetic moment induced is small) in the same direction as that of applied magnetic field, so magnet attracts $N_2$ weakly.
Diamagnetic substances also get weakly magnetised when placed in an external magnetic field but in opposite direction and hence, $N_3$ is weakly repelled by magnet.