More about Magnetic Dipoles

Q.

What is the Meissner effect?

Q. A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in equilibrium state. The energy required to rotate it by $60°$ is $W$. Now the torque required to keep the magnet in this new position is

1. $\frac{\sqrt{3}W}{2}$
2. $\frac{2W}{\sqrt{3}}$
3. $\frac{W}{\sqrt{3}}$
4. $\sqrt{3}W$

Q.

The value of the horizontal component of the earth's magnetic field and angle of dip are $1.8\times {10}^{-5}Weber/m^2$ and ${30}^0$ respectively at some place. The total intensity of earth's magnetic field at that place will be

1. $3.18\times {10}^{-5}Weber/m^2$
2. $3.67\times {10}^{-5}Weber/m^2$
3. $5.0\times {10}^{-5}Weber/m^2$
4. $2.08\times {10}^{-5}Weber/m^2$
   

Q.

A circular coil of wire consisting of 100 turns, each of radius 8.0 cm carries a current of 0.40 A. What is the magnitude of the magnetic field B at the centre of the coil?

Q. In Rutherford experiments on $\alpha$-ray scattering the number of particles scattered at ${90}^{\circ }$ be 28 per minute. Then the number of particles scattered per minute by the same foil, but at ${60}^{\circ }$ is

1. 112
2. 60
3. 56
4. 120

Q.

A long straight wire carries a current of 35 A. What is the magnitude of the field B at a point 20 cm from the wire?

Q. A sphere of radius R is placed in uniform electric field E.The inward electric flux through the sphere is?

Q. The surface of a metal is illuminated alternately with photons of energies $E_1=4\text{eV}$ and $E_2=2.5\text{eV}$ respectilvely. The ratio of maximum speeds of the photoelectrons emitted in two cases is $2$. The work function of metal in $\left(\text{eV}\right)$ is

Q.

A short bar magnet placed with its axis at 30º with a uniform external magnetic field of 0.25 T experiences a torque of magnitude equal to 4.5 × 10⁻² J. What is the magnitude of magnetic moment of the magnet?

Q.

A circular coil of radius 4 cm and of 20 turns carries a current of 3 amperes. It is placed in a magnetic field of intensity of 0.5 . The magnetic dipole moment of the coil is

1. 
   

2. 
   

3. 
   

4. 
   

Q. An inductor coil stores $64\text{J}$ of magnetic field energy and dissipates energy at the rate of $640\text{W}$ when a current of $8\text{A}$ is passed through it. If this coil is joined across an ideal battery, find the time constant of the circuit, in seconds.

1. $0.8$
2. $0.4$
3. $0.80$
4. $0.2$

Q. A magnetic field of $2\times {10}^{-2}T$ acts at right angles to a coil of area $100c{m}^2$, with $50$ turns. The average e.m.f. induced in the coil is $0.1V$, when it is removed from the field in $t$ $sec$. The value of $t$ is

1. $10s$
2. $0.1s$
3. $0.01s$
4. $10s$

Q. The magnetic field associated with a light waves given at the origin by $B=B_0\left[\sin \right(3.14\times {10}^7)\text{ct}+\sin (6.28\times {10}^7\left)\text{ct}\right]$
If this light falls on a silver plate having a work function of $4.7\text{eV}$, What will be the maximum kinetic energy of the photoelectrons?

($c=3\times {10}^8{\text{ms}}^{-1},h=6.6\times {10}^{-34}\text{J-s})$

1. $\text{8.52 eV}$
2. $\text{7.72 eV}$
3. $\text{12.5 eV}$
4. $\text{6.82 eV}$

Q. A thin disc of radius $b=2a$ has concentric hole of radius ‘$a$’ in it (see figure). It carries uniform surface charge ‘$\sigma$’ on it. If the electric field on its axis at height ‘$h$’ $(h<<a)$ from its centre is given as ‘$Ch$’, then value of ‘$C$’ is:

1. $\frac{\sigma }{4a{\epsilon }_0}$
2. $\frac{\sigma }{2a{\epsilon }_0}$
3. $\frac{\sigma }{8a{\epsilon }_0}$
4. $\frac{\sigma }{a{\epsilon }_0}$

Q. A non-conducting rod $AB$ of length $l$ has a total charge $q$. The rod is rotated about an axis passing through its center of mass with a constant angular velocity $\omega$ as shown in the figure. The magnetic moment of the rod is

1. $\frac{q\omega l^2}{12}$
2. $\frac{q\omega l^2}{3}$
3. $\frac{q\omega l^2}{24}$
4. $\frac{q\omega l^2}{6}$

Q. An insulating rod of length L carries a charge $q$ distributed uniformly on it. The rod is pivoted at its mid-point and is rotated at a frequency f about a fixed axis perpendicular to the rod and passing through the pivot. The magnetic moment of the rod system is

1. $\pi qf{l}^2$
2. $\frac{1}{12}\pi qf{l}^2$
3. $\frac{1}{6}\pi qf{l}^2$
4. $\frac{1}{3}\pi qf{l}^2$

Q. A conducting wire bent in the shape of a parabola $y^2=2x$ carries a current of $2\text{A}$ as shown. This wire is placed in a uniform magnetic field $\overrightarrow{B}=-4\hat{k}$. The magnitude of force on the wire is (Give integer value)

Q. A thin magnetic needle oscillates in the horizontal plane with a time period of $2.0$ sec. If the needle is broken into $4$ equal parts perpendiculars to its length, then the time period (in second) of each part will be

Q. Two short bar magnets of magnetic moments $‘M^{\prime }$ each are arranged at the opposite corners of a square of side $‘d^{\prime }$ such that their centres coincide with the corners and their axes are parallel to one side of the square. If the like poles are in the same direction, the magnetic induction at any of the other corners of the square is.

1. $\frac{{\mu }_{o}M}{4\pi d^3}$
2. $\frac{{\mu }_{o}M}{2\pi d^3}$
3. $\frac{{\mu }_{o}2M}{4\pi d^3}$
4. $\frac{{\mu }_{o}2M}{2\pi d^3}$

Q. Magnitude of magnetic dipole moment of loop as shown in figure is? Each curve is of radius R.

1. $\pi R^{2}i$
2. $2\pi R^{2}i$
3. $\frac{\pi R^{2}i}{2}$
4. $\frac{3}{4}\pi R^{2}i$

Q.

A bar magnet of magnetic moment 1.5 J T⁻¹ lies aligned with the direction of a uniform magnetic field of 0.22 T.

(a) What is the amount of work required by an external torque to turn the magnet so as to align its magnetic moment: (i) normal to the field direction, (ii) opposite to the field direction?

(b) What is the torque on the magnet in cases (i) and (ii)?

Q. A short bar magnet of magnetic moment m = 0.32 JT–1 is placed in auniform magnetic field of 0.15 T. If the bar is free to rotate in the plane of the field, which orientation would correspond to its (a) stable, and (b) unstable equilibrium? What is the potential energy of themagnet in each case?

Q. The current in the winding of a toroid is $2.0\text{A}$. There are $400$ turns and the mean circumferential length is $40\text{cm}$. If the magnetic field inside the toroid is $0.5\text{T}$, the permeability is nearly:

1. $5\times {10}^{-4}\text{Wb/A-m}$
2. $25\times {10}^{-4}\text{Wb/A-m}$
3. $2.5\times {10}^{-4}\text{Wb/A-m}$
4. $1.25\times {10}^{-4}\text{Wb/A-m}$

Q. Each side of cube is L then magnitude of magnetic dipole moment of loop oabcdeo carrying current i as shown in figure is.

1. $i{L}^2$
2. $\sqrt{2}i{L}^2$
3. $\sqrt{3}i{L}^2$
4. $0$

Q. The time period of a thin magnet in earth's magnetic field is $T$. If the magnet is cut into two equal parts perpendicular to its length, the time period of each part in the same field will be

1. $\sqrt{2T}$
2. $2T$
3. $T$
4. $\frac{T}{2}$

Q.

A magnetic dipole is under the influence of two magnetic fields. The angle between the field directions is 60º, and one of the fields has a magnitude of 1.2 × 10⁻² T. If the dipole comes to stable equilibrium at an angle of 15º with this field, what is the magnitude of the other field?

Q.

On what factors does the magnetic field strength of a current-carrying coil depend?

Q. If the coercivity of iron is 2000 ampere per metre then magnetic field is explain clearly

Q. The dip at a place is $\delta .$ For measuring it, the axis of the dip needle is perpendicular to the magnetic meridian. If the axis of the dip needle makes angle $\theta$ with the magnetic meridian, the apparent dip will be given $\tan {\delta }_1$ which is equal to

1. $\tan \delta cose\theta$
2. $\tan \delta \sec \theta$
3. $\tan \delta \sin \theta$
4. $\tan \delta \cos \theta$

Q. A circular coil of radius 4 cm has 50 turns. In this coil a current of 2 A is flowing. It is placed in a magnetic field of $0.1weber/m^2$. The amount of work done in rotating it through ${180}^{\circ }$ from its equilibrium position will be

1. 0.1 J
2. 0.2 J
3. 0.5 J
4. 0.8 J