Magnetism Questions

The materials suitable for making electromagnets should have:

The length of a magnet is large compared to its width and breadth. The time period of its oscillation in a vibration magnetometer is $2\text{s}$. The magnet is cut along its length into three equal parts and three parts are then placed on each other with their like poles together. The time period of this combination will be:

Two long conductors, separated by a distance $d$ carry current $I_1$ and $I_2$ in the same direction. They exert a force $F$ on each other. Now the current in one of them increased to two times and its direction reversed. The distance is also increased to $3d$. The new value of the force between them is:

The magnetic field due to a current carrying circular loop of radius $3\text{cm}$ at a point on the axis at a distance of $4\text{cm}$ from the centre is $54\mu \text{T}$. What will be its value at the centre of the loop?

A long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is $B$. It is then bent into a circular loop of $n$ turns. The magnetic field at the centre of the coil will be:

A current $I$ ampere flows along an infinitely long straight thin walled tube, then the magnetic induction at any point inside the tube is:

A long solenoid has $200$ turns per cm and carries a current $i$. The magnetic field at its centre is $6.28\times 10^{-2}{\text{Wb/m}}^2$. Another long solenoid has $100$ turns per cm and it carries a current $i/3$. The value of the magnetic field at its centre is:

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:

In a region, steady and uniform electric and magnetic fields are present. These two fields are parallel to each other. A charged particle is released from rest in this region. The path of the particle will be a:

When the current changes from $+2\text{A}$ to $-2\text{A}$ in $0.05$ second, an e.m.f. of $8\text{V}$ is induced in a coil. The coefficient of self-induction of the coil is:

Proton, Deuteron and alpha particle of the same kinetic energy are moving in circular trajectories in a constant magnetic field. The radii of proton, deuteron and alpha particle are respectively $r_p$, $r_d$ and $r_{\alpha }$. Which one of the following relations is correct?

A charge $Q$ is uniformly distributed over the surface of non-conducting disc of radius $R$. The disc rotates about an axis perpendicular to its plane and passing through its centre with an angular velocity $\omega$. As a result of this rotation a magnetic field of induction $B$ is obtained at the centre of the disc. If we keep both the amount of charge placed on the disc and its angular velocity to be constant and vary the radius of the disc then the variation of the magnetic induction at the centre of the disc will be represented by:

A current $I$ flows in an infinitely long wire with cross section in the form of a semicircular ring of radius $R$. The magnitude of the magnetic induction along its axis is:

A boat is moving due east in a region where the earth's magnetic field is $5.0\times 10^{-5}{\text{NA}}^{-1}{\text{m}}^{-1}$ due north and horizontal. The boat carries a vertical aerial $2\text{m}$ long. If the speed of the boat is $1.50{\text{ms}}^{-1}$, the magnitude of the induced emf in the wire of aerial is:

Two long parallel wires are at a distance $2d$ apart. They carry steady equal current $I$ flowing out of the plane of the paper. The variation of the magnetic field $B$ along the line $X{X}^{\prime }$ (perpendicular to wires) is zero at what point?

Relative permittivity and permeability of a material are ${ϵ}_r$ and ${\mu }_r$. Which values are allowed for a diamagnetic material?

One conducting U-tube can slide inside another as shown in figure, maintaining electrical contacts between the tubes. The magnetic field $B$ is perpendicular to the plane of the figure. If each tube moves towards the other at a constant speed $V$, then the emf induced in the circuit in terms of $B,l$ and $V$ where $l$ is the width of each tube will be:

A thin rectangular magnet suspended freely has a period of oscillation equal to $T$. Now it is broken into two equal halves (each having half of the original length) and one piece is made to oscillate freely in the same field. If its period of oscillation is $T^{\prime }$, the ratio $T^{\prime }/T$ is:

Curie temperature is the temperature above which:

The core of any transformer is laminated so as to:

The magnetic lines of force inside a bar magnet:

A particle of mass $M$ and charge $Q$ moving with velocity $\vec{v}$ describes a circular path of radius $R$ when subjected to a uniform transverse magnetic field of induction $B$. The work done by the field when the particle completes one full circle is:

Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon:

A magnetic needle lying parallel to a magnetic field requires $W$ units of work to turn it through $60^{\circ }$. The torque needed to maintain the needle in this position will be:

A magnetic needle is kept in a non-uniform magnetic field. It experiences:

A charged particle of mass $m$ and charge $q$ travels on a circular path of radius $r$ that is perpendicular to a magnetic field $B$. The time taken by the particle to complete one revolution is:

A uniform electric field and a uniform magnetic field are acting along the same direction in a certain region. If an electron is projected along the direction of the fields with a certain velocity then:

The self inductance of the motor of an electric fan is $10\text{ H}$. In order to impart maximum power at $50\text{ Hz}$, it should be connected to a capacitance of:

A coil of inductance $300\text{ mH}$ and resistance $2\Omega$ is connected to a source of voltage $2\text{V}$. The current reaches half of its steady state value in:

Two concentric coils each of radius equal to $2\pi \text{ cm}$ are placed at right angles to each other. $3\text{ Ampere}$ and $4\text{ ampere}$ are the currents flowing in each coil respectively. The magnetic induction in Weber/m${}^2$ at the centre of the coils will be (${\mu }_0=4\pi \times 10^{-7}$ W/A-m):

Two thin, long parallel wires separated by a distance ‘$d$ ’ carry a current of ‘$i$ ’ A in the same direction. They will: