Question

There are four light-weight-rod samples; $A,B,C,D$ separately suspended by threads. A bar magnet is slowly brought near each sample and the following observations are noted:
$\left(i\right)A$ is feebly repelled
$\left(ii\right)B$ is feebly attracted
$\left(iii\right)C$ is strongly attracted
$\left(iv\right)D$ remains unaffected

​​​​​​​Which one of the following is true?

• A.
  $C$ is of a diamagnetic material.
• B.
  $D$ is of a ferromagnetic material.
• C.
  $A$ is of a non-magnetic material.
• D.
  $B$ is of a paramagnetic material.

Answer 1

The correct option is D

$B$ is of a paramagnetic material.
Since, $A$ is feebly repelled:
$\Rightarrow \text{A develops weak magnetization opposite}\text{to external field}\Rightarrow \text{A is dia-magnetic in nature.}$

$B$ is feebly attracted:
$\Rightarrow \text{B develops weak magnetization in}\text{the direction of external field}$
$B$ is of a paramagnetic material.

$C$ is strongly attracted:
$\Rightarrow \text{C develops strong magnetization}\text{along the external field}\Rightarrow \text{C must be ferromagnetic in nature.}$

Hence, $\left(D\right)$ is the correct answer.