Umakant Kondapure, Collin Fernandes, Nipun Bhatia, Vikram Bathula and, Ketki Deshpande Solutions for Chapter: Magnetism, Exercise 4: Evaluation Test

The most appropriate $I-H$ curve for a paramagnetic substance is

A bar magnet having coercivity $4\times {10}^3 \mathrm{A} {\mathrm{m}}^{-1}$ is demagnetised by inserting it inside a solenoid $10 \mathrm{cm}$ long and having $50$ turns. The current that should be sent through the solenoid is
 

A cylindrical rod magnet having length of $4 \mathrm{cm}$ and a diameter of $1.2 \mathrm{cm}$ has a uniform magnetization of $4.20\times {10}^3 \mathrm{A} {\mathrm{m}}^{-2}$. Its magnetic dipole moment is
 

Select the correct option:
i. Susceptibility of a diamagnetic substance is high and negative.
ii. In paramagnetic substance, the intrinsic magnetic moment is not zero.
iii. When a paramagnetic substance is heated, it becomes ferromagnetic.
iv. Spin exchange interaction is present in the absence of external magnetic field.
 

A toroid has $1500 \mathrm{turns}$ and the inner and outer radii of its core $6 \mathrm{cm}$ and $8 \mathrm{cm}$ respectively. The magnetic field in the core for a current of $0.5 \mathrm{A}$ is $2 \mathrm{T}$. The relative permeability of core is
 

An iron rod of volume ${10}^{-4}{\mathrm{m}}^3$ and relative permeability $900$ is placed inside a long solenoid wound with $6 \text{turns per} \mathrm{cm}$. If a current of $0.4\mathrm{A}$ is passed through the solenoid, the magnetic moment of the rod is
 

A small coil $C$ with $N=100$ turns is mounted on one end of a balance beam and introduced between the poles of an electromagnet as shown in the figure. The cross-sectional area of coil is $\mathrm{A}=1.0 {\mathrm{cm}}^2$, length of the arm $OA$ of the balance beam is, $l=20\mathrm{cm}$. When there is no current in the coil, the balance is in equilibrium. On passing a current $i=18 A$ through the coil, the equilibrium is restored by putting the additional counter weight of mass $\mathrm{\Delta m}=40 \mathrm{gm}$ on the balance pan. Find the magnetic induction at the spot where coil is located.

Assertion: Any instrument can be protected from an external magnetic field by putting it inside a wooden box.

Reason: Iron is a magnetic substance.