∮ B → · d s → = 0 equation is not according to the following

The number of magnetic lines leaving a surface is not equal to that of entering the surface.

The net magnetic flux enclosed by any closed surface is zero.

No isolated magnetic poles are available.

The magnetic flux is positive at some place and it is negative at some other place.

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The best material to make permanent magnets is

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Important Questions on Matter and Magnetism

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

A small bar magnet is placed with its axis at

30^{o}

with an external magnetic field of

0.06 T

experiences a torque of

0.018 Nm

. The minimum work required to rotate it from its stable to unstable equilibrium position is:

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

A circular coil having

N

turns and radius

r

carries a current

I .

It is held in the

X Z

plane in a magnetic field

B \hat{i}

. The torque on the coil due to the magnetic field is:

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

An electron gun is placed inside a long solenoid of radius

R

on its axis. The solenoid has

n

turns/length and carries a current

I .

The electron gun shoots an electron along the radius of the solenoid with speed

v .

If the electron does not hit the surface of the solenoid, maximum possible value of

v

is (all symbols have their standard meaning):

Question Image

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

\oint \vec{B} \cdot d \vec{s} = 0

equation is not according to the following

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

An insulating thin rod of length

l

has a linear charge density

ρ (x) = ρ_{0} \frac{x}{l}

on it. The rod is rotated about an axis passing through the origin

(x = 0)

and perpendicular to the rod. If the rod makes

n

rotations per second, then the time averaged magnetic moment of the rod is:

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

A thin rod of length

L

is magnetized and has magnetic moment

M

. The rod is then bent in a semicircular arc. The magnetic moment in the new shape is

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

The magnetic dipole moment of a short magnetic dipole at a distant point along the equator of magnet has a magnitude of

X

in SI units. If the distance between point and the magnet is halved then the magnitude of dipole moment will be

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

A bar magnet of length

14 cm

is placed in the magnetic meridian with its north pole pointing towards the geographic north pole. A neutral point is obtained at a distance of

18 cm

from the center of the magnet. If

B_{H} = 0.4 G

, the magnetic moment of the magnet is

(1 G = 10^{- 4} T)

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

Two short bar magnets of length

1 cm

each have magnetic moments

1 .20 A m^{2}

and

1 .00 A m^{2}

respectively. They are placed on a horizontal table parallel to each other with their

N

poles pointing towards the south. They have a common magnetic equator and are separated by a distance of

20 .0 cm

. The value of the resultant horizontal magnetic induction at the mid-point

O

of the line joining their centres is close to
( Horizontal component of earth's magnetic induction is

3 .6 \times 10^{- 5} Wb m^{- 2}

)

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

The magnetic flux near the axis and inside the air-core solenoid of length

60 cm

carrying current

I

1.57 \times 10^{6} Wb .

Its magnetic moment will be (cross-sectional area of a solenoid is very small as compared to its length,

μ_{0} = 4 π \times 10^{- 7}

SI units)

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

Inside a bar magnet, the magnetic lines of force

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

Electromagnets are made of soft iron because, soft iron has

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

Two short bar magnets of moments

512 A m^{2}

and

1000 A m^{2}

are placed coaxially

18 cm

apart. The magnetic field is zero at a point

Q

between them. The field at

Q

, when one of the magnets is reversed pole to pole is

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

An electron is moving along

+ x

direction with a velocity of

6 \times 10^{6} {ms}^{- 1}

. It enters a region of uniform electric field of

300 V / c m

pointing along

+ y

direction. The magnitude and direction of the magnetic field set up in this region such that the electron keeps moving along the x direction will be:

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

A magnet of pole strength

m

and length

l

is broken into two pieces. The pole strength of each piece is

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

A large magnet is broken into two pieces so that their lengths are in the ratio

1 : 2

. The ratio of their magnetic moments is

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

Which of the following statements are correct?
(A) Electric monopoles do not exist whereas magnetic monopoles exist.
(B) Magnetic field lines due to a solenoid at its ends and outside cannot be completely straight and confined.
(C) Magnetic field lines are completely confined within a toroid.
(D) Magnetic field lines inside a bar magnet are not parallel.
(E) $χ = - 1$ is the condition for a perfect diamagnetic material, where $χ$ is its magnetic susceptibility.

Choose the correct answer from the options given below :

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

Two identical bar magnets are held perpendicular to each other with a certain separation, as shown below. The area around the magnets is divided into four zones.
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Given that there is a neutral point it is located in,

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

A hoop and a solid cylinder of same mass and radius are made of a permanent magnetic material with their respective axes. But the magnetic moment of hoop is twice of solid cylinder. They are placed in a uniform magnetic field in such a manner that their magnetic moments make a small angle with the field. If the oscillation periods of hoop and cylinder are

T_{h}

and

T_{c}

respectively, then:

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Physics>Electricity and Magnetism>Matter and Magnetism>Bar magnet

In a permanent magnet at room temperature

The best material to make permanent magnets is

Important Questions on Matter and Magnetism

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