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CBSE Questions for Class 12 Medical Physics Magnetism And Matter Quiz 13 - MCQExams.com
CBSE
Class 12 Medical Physics
Magnetism And Matter
Quiz 13
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Diamagnetism occurs in all materials.
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Diamagnetism results from the partial alignment of permanent magnetic moment.
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The magnetizing field intensity H is always zero in free space.
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The magnetic field of induced magnetic moment is opposite to the applied field.
A paramagnetic material is placed in a magnetic field. Consider the following statements:
(A) If the magnetic field is increased, the magnetization is increased.
(B) If the temperature is increased, the magnetization is increased
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Both A and B are true.
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A is true but B is false.
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B is true but A is false.
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Both A and B are false.
S is the surface of a lump of magnetic material.
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Lines of B are necessarily continuous across S.
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Some lines of B must be discontinuous across S.
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Lines of H are necessarily continuous across S.
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Lines of H cannot all be continuous across S.
Explanation
Magnetic field lines for magnetic induction (B) from continuous lines so lines of B are necessarily continuous across S.
Also magnetic intensity (H) to magnetisation varies for inside and outside the lump.
So line of H cannot all be continuous across S.
Consider the two idealized systems: (i) a parallel plate capacitor with large plates and small separation and (ii) a long solenoid of length $$ L> > R $$, radius of cross- section. In (i) E is ideally treated as a constant between plates and zero outside. In (ii) magnetic field is constant inside the solenoid and zero outside. These idealized assumptions, however, contradict fundamental laws as below:
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case (i) contradicts Gauss's law for electrostatic fields.
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case (ii) contradicts Gauss's law for magnetic fields.
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case (i) agrees with $$ \oint _{s} E. dl = 0 $$
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case (ii) contradicts $$ \oint H . dl = I_{4n} $$
Explanation
According to Gauss's law of electrostatic field
$$ \oint _{s} E. ds = \dfrac{q}{\varepsilon _{0}} $$
so it does not contradicts for electrostatic field as the electric field lines do not from continuous path.
According to Gauss's law of magnetic field $$ \oint _{s} B. ds = 0 $$.
It contradicts for magnetic field. because there is magnetic field inside the solenoid , and no field outside the solenoid carrying current, but the magnetic field lines from the closed paths.
The primary origin (s) of magnetism lies in
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atomic currents.
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Pauli exclusion principle.
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polar nature of molecules.
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intrinsic spin of electron.
Explanation
Motion charges particle produces magnetism and nature of magnetism depends on the nature of the motion of a charged particle. In atom, electron revolve and spin around the nucleus which in turn produces current and due to magnetic effect of current, magnetism produces in the material.
Select the correct answer.
If we suspend a magnet freely, it will settle in.
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east-west direction
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north-south direction
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north-east direction
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east-south direction
Explanation
Because of the earth's magnetic field, the magnetic field of the earth's metallic core aligns its North toward the actual north. So a freely suspended magnet would align itself northwards towards the North of the earth's magnet. Actually it faces towards the north-south poles of earth.
In a uniform magnetic field, the field lines are:
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curved
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parallel and equidistant straight lines
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parallel, but non-equidistant straight lines
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nothing can be said
Explanation
Parallel and equidistant straight lines.
The earth’s magnetic field in a limited space is uniform.
Two small bar magnets are placed in a line with like poles facing each other at a certain distance $$ d $$ apart. If the length of each magnet is negligible as compared to $$ d $$, the force between them will be inversely proportional to
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$$ d $$
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$$ d^2 $$
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$$ \frac{1}{d^2} $$
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$$ d^4 $$
Explanation
Two small bar magnets are placed in a line with like poles facing each other at a certain distance $$ d $$ apart. If the length of each magnet is negligible as compared to $$ d $$, the force between them is given by:-
$$F = \dfrac{\mu_0}{4 \pi} \dfrac{(6MM')}{d^4}$$ $$\Rightarrow$$ $$ F \propto \dfrac{1}{d^4}$$
A uniform magnetic field, parallel to the plane of the paper existed in space initially directed from left to right. When a bar of soft iron is placed in the field parallel to it, the lines of force passing through it will be represented by
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Figure (A)
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Figure (B)
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Figure (C)
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Figure (D)
Explanation
Permeability of soft iron is maximum, so maximum lines of force tries to pass through the soft iron.
Two magnetic lines of force due to a bar magnet
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Intersect at the neutral point
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Intersect near the poles of the magnet
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Intersect on the equatorial axis of the magnet
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Do not intersect at all
Explanation
The two magnetic lines of force due to a bar magnet do not intersect each other because, at the point of intersection, the compass needle would point towards two directions, which is not possible.
At a certain place the horizontal component of the earths magnetic field is $$ B^0 $$ and the angle of dip is $$ 45^0 $$ . The total intensity of the field at that place will be
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$$ B $$
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$$ \sqrt {2} B_0 $$
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$$ 2 B $$
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$$ B^2_0 $$
Explanation
According to the question $$ B_H = B sin \phi \Rightarrow B = \dfrac {B_H}{sin \phi} = \dfrac{B_o}{sin45^o} = \sqrt {2} B_0 $$
Moment of inertia of a magnetic needle is $$ 40 gm-cm^2 $$ has time period 3 seconds in earth's horizontal field = $$ 3.6 \times 10^{-5} $$ weber/m. Its magnetic moment will be
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$$ 0.5 A \times m^2 $$
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$$ 5 A \times m^2 $$
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$$ 0.250 A \times m^2 $$
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$$ 5 \times 10^2 A \times m^2 $$
Explanation
$$ T = 2\pi \sqrt { \dfrac {I}{ MB_H}}$$
$$ I = 40gm - cm^2 = 400 \times 10^{-8} kg -m^2 $$
$$ \therefore 3 = 2\pi \sqrt { \dfrac { 400 \times 10^{-8} }{ 36 \times 10^{-6} \times M } } $$
$$ \Rightarrow \dfrac {1}{M} = \dfrac {9}{ 4 \pi^2} \times \dfrac {36}{4} \Rightarrow M = 0.5 \times A \times m^2 $$
Diamagnetic substances are
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Feebly attracted by magnets
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Strongly attracted by magnets
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Feebly repelled by magnets
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Strongly repelled by magnets
Explanation
Diamagnetic materials are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force.
The time period of a bar magnet suspended horizontally in the earth's magnetic field and allowed to oscillate
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Is directly proportional to the square root of its mass
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Is directly proportional to its pole strength
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Is inversely proportional to its magnetic moment
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Decreases if the length increases but pole strength remains same
Explanation
We know that when a bar magnet suspended horizontally in the earth's magnetic field and allowed to oscillate, time period is given by:-
$$ T = 2 \pi \sqrt { \dfrac {(I)}{(M)B_H} } $$
$$ T \propto \dfrac{1}{ \sqrt{M}}$$
Substances in which the magnetic moment of a single atom is not zero, is known as
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Diamagnetism
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Ferromagnetism
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Paramagnetism
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Ferrimagnetism
Explanation
The property of paramagnetism is found in these substances whose atoms have an excess of electrons spinning in the same direction. Hence atoms of paramagnetic substances have a net non-zero magnetic moment of their own.
The magnetic susceptibility does not depend upon the temperature in
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Ferrite substances
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Ferromagnetic substances
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Diamagnetic substances
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Paramagnetic substances
Explanation
The magnetic susceptibility does not depend upon the temperature in Diamagnetic substances.
The magnetic susceptibility is
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$$ x = \frac {1}{H} $$
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$$ x = \frac {B}{H} $$
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$$ x = \frac {M}{V} $$
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$$ x = \frac {M}{H} $$
Explanation
Magnetic susceptibility is a dimensionless proportionality constant that indicates the degree of magnetization of a material in response to an applied magnetic field. It is caused by interactions of electrons and nuclei with the externally applied magnetic field.
The mathematical definition of magnetic susceptibility is the ratio of magnetization to applied magnetizing field intensity. This is a dimensionless quantity. i.e $$X = \dfrac{M}{H}$$
Which of the following statements are true about the magnetic susceptibility $$ x_m $$of paramagnetic substance
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Value of $$ X_m $$is inversely proportional to the absolute temperature of the sample
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$$ X_0 $$ is positive at all temperature
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$$ X_m $$ is negative at all temperature
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$$ X_m $$does not depend on the temperature of the sample
Explanation
Since it is the ratio of two magnetic fields, susceptibility is a dimensionless number. Diamagnetic substances have negative susceptibilities $$(χ < 0)$$; paramagnetic, superparamagnetic, and ferromagnetic substances have positive susceptibilities $$(χ > 0)$$.
For paramagnetic substance value of $$χ_m$$ is inversely proportional to the absolute temperature of the sample
Which of the following is true
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Diamagnetism is temperature dependent
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Paramagnetism is temperature dependent
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Paramagnetism is temperature independent
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None of these
Explanation
Paramagnetism is temperature dependent
Which of the following statements is incorrect about hysteresis
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This effect is common to all ferromagnetic substances
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The hysteresis loop area is proportional to the thermal energy developed per unit volume of the material
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The hysteresis loop area is independent of the thermal energy developed per unit volume of the material
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The shape of the hysteresis loop is characteristic of the material
Explanation
The energy lost per unit volume of a substance in a complete cycle of magnetisation is equal to the area of the hysteresis loop.
The universal property of all substances is
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$$ Diamagnetism $$
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$$ Ferromagnetism $$
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$$ Paramagnetism $$
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All of these
Explanation
The universal property of all substances is Diamagnetism.
Identify the paramagnetic substance
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Iron
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Aluminium
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Nickel
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Hydrogen
Explanation
Aluminium is a paramagnetic substance.
The use of study of hysteresis curve for a given material is to estimate the
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Voltage loss
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Hysteresis loss
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Current loss
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All of these
Explanation
The use of study of hysteresis curve for a given material is to estimate the Hysteresis loss.
The magnetic susceptibility is negative for
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Paramagnetic materials
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Diamagnetic materials
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Ferromagnetic materials
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Paramagnetic and ferromagnetic materials
Explanation
The magnetic susceptibility is negative for Diamagnetic materials.
An example of a diamagnetic substance is
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Aluminium
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Copper
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Iron
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Nickel
Explanation
An example of a diamagnetic substance is Copper.
A frog can be deviated in a magnetic field produced by a current in a vertical solenoid placed below the frog. This is possible because the body of the frog behaves as
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$$ Paramagnetic $$
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$$ Diamagnetic $$
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$$ Ferromagnetic $$
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$$ Antiferromagnetic $$
Explanation
A frog can be deviated in a magnetic field produced by a current in a vertical solenoid placed below the frog. This is possible because the body of the frog behaves as diamagnetic substances because diamagnetic substances are repelled by the magnetic field.
Curie-Weiss law is obeyed by iron at a temperature ......
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Below Curie temperature
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Above Curie temperature
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At Curie temperature only
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At all temperatures
Explanation
Curie-Weiss law is obeyed by iron at a temperature above its curie temperature.
The magnetic susceptibility of any paramagnetic material changes with absolute temperature T as
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Directly proportional to T
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Remains constant
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Inversely proportional to T
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Exponentially decaying with T
Explanation
The magnetic susceptibility of any paramagnetic material changes with absolute temperature $$T$$ as it is inversely proportional to $$T$$.
When a ferromagnetic material is heated to temperature above its Curie temperature, the material
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Is permanently magnetized
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Remains ferromagnetic
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Behaves like a diamagnetic material
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Behaves like a paramagnetic material
Explanation
When a ferromagnetic material in heated above its curie temperature then it behaves like paramagnetic material.
Curies law can be written as
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$$ X \propto (T-T_c) $$
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$$ X \propto \frac {1}{ T -T_c} $$
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$$ X \propto \frac {1}{T} $$
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$$ X \propto T $$
Explanation
The curie law states that in a paramagnetic material, the material's magnetization is directly proportional to an applied magnetic field. This relationship is defined as the Curie's law. The constant $$'C'$$ is called the curie constant. The equation may also be modified to $$χ = C/ (T − θ)$$, where $$θ$$ is a constant.
A diamagnetic material in a magnetic field moves
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From weaker to the stronger parts of the field
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Perpendicular to the field
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From stronger to the weaker parts of the field
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In none of the above directions
Explanation
A diamagnetic material in a magnetic field moves from stronger to the weaker parts of the field.
A superconductor exhibits perfect
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$$ Ferrimagnetism $$
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$$ Ferromagnetism $$
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$$ Paramagnetism $$
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$$ Diamagnetism $$
Explanation
A superconductor exhibits perfect diamagnetism.
Which of the following is diamagnetism
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$$ Aluminium $$
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$$ Quartz $$
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$$ Nickel $$
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$$ Bismuth $$
Explanation
Bismuth is diamagnetism.
For substances hysteresis $$ (B - H) $$ curves are given as shown in figure. For making temporary magnet which of the following is best.
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Explanation
For a temporary magnet the hysteresis loop should be long and narrow.
Hence option $$D$$ is correct.
The variation of magnetic susceptibility $$ (\chi) $$ with magnetising field for a paramagnetic substance is
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Explanation
Susceptibility of a paramagnetic substance is independent of magnetising field.
The variation of magnetic susceptibility $$ (\chi) $$ with absolut temperature $$ T $$ for a ferromagnetic material is
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Explanation
Susceptibility of a ferromagnetic substance falls with rise of temperature $$ \left( \chi =\dfrac { c }{ T-{ T }_{ c } } \right) $$ and the substance becomes paramagnetic above curie temperature, so magnetic susceptibility becomes very small above curie temperature.
Magnetic susceptibility is negative and very less for :
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ferromagnetic substances
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paramagnetic substances
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diamagnetic substance
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all of the above
Explanation
Magnetic susceptibility is negative and very less for diamagnetic substances.
Magnetic moment of diamagnetic substances is
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infinity
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zero
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$$100 Am^{2}$$
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none of these
Explanation
Magnetic moment of diamagnetic substance is zero.
The most appropriate magnetization $$ M $$ versus magnetising field $$ H $$ curve for a paramagnetic substance is
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$$ A $$
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$$ B $$
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$$ C $$
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$$ D $$
Explanation
For paramagnetic substance magnetization $$ M $$ proportional to magnetising field $$ H $$, and $$ M $$ is positive. Hence option $$A$$ is correct.
If the distance between two magnetic poles of unit magnetic strength is $$1 m$$, then force acting between them will be:
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$$4\pi \times 10^{-7}N$$
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$$4\pi N$$
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$$10^{-7}N$$
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$$\frac{4\pi}{10^{-7}}N$$
Explanation
$$m_{1}=m_{2}=1; r=1\,m$$
$$F=\dfrac{\mu_{0}}{4\pi} \dfrac{m_{1}m_{2}}{r_{2}}$$
$$F=\dfrac{\mu_{0}}{4\pi} \frac{1 \times 1}{1}$$
$$\Rightarrow F=\dfrac{\mu_{0}}{4\pi} =\dfrac{4\pi \times 10^{-7}}{4\pi}=10^{-7}N$$
In which of the following, the magnetic field does not interplay with :
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magnet
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accelerated magnet
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static charge
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dynamic charge
Explanation
Magnetic field does not interact with static charges.
The cause of dimegnetism is :
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orbital motion of electrons
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spin motion of electrons
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paired electrons
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none of the above
Explanation
Due to orbital motion of electrons.
For ferromagnetic material, the relative permeability $$ ( \mu_r) $$ , versus magnetic intensity $$ (H) $$ has the following shape
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Explanation
$$ \mu_r=1+\dfrac{1}{H}; $$ as we know $$ I $$ dependent on $$ H $$, initially value of $$ \dfrac{I}{H}$$ is smaller so value of $$ \mu $$ increases with $$H $$ but slowly but with further increases of $$H$$ value of $$\dfrac{I}{H} $$ also increases i.e. $$ \mu $$ increases speedily. When material fully magnetised $$I$$ becomes constant then with the increase of $$H$$ ($$\dfrac{1}{H} $$ decreases) $$ \mu $$ decreases, This is confirm field with the option (d).
The figure illustrate how $$ B $$, the flux density inside a sample of unmagnetised ferromagnetic material varies with $$ B_0 $$ , the magnetic flux density in which the sample is kept. For the sample to be suitable for making a permanent magnet
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$$ OQ $$ should be large, OR should be small
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$$ OQ $$ and OR should both be large
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$$ OQ $$ should be small and OR should be large
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$$ OQ $$ and OR should both be small
Explanation
In the given figure $$ OQ $$ refers to retentivity while $$ OR $$ refers to corecivity, for permanents both retentivity and corecivity should be high.
The basic magnetization curve for a ferromagnetic material is shown in figure. Then, the value of relative permeability is highest for the point
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$$ P $$
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$$ Q $$
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$$ R $$
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$$ S $$
Explanation
$$ B= \mu_0\mu_rH \Rightarrow \mu_r \propto \dfrac{B}{H}$$ = slope $$ B-H $$ curve According to the given graph, slope of the graph is highest point $$ Q$$.
Area of hysteresis loop of any substance represent:
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energy loss in magnetising a substance in unit cycle
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energy loss in magnetising unit volume in unit cycle
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energy loss in magnetising a substance for unit volume
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energy loss in magnetising a substance
Explanation
Area of hysteresis loop of any substance represent energy loss in magnetising a substance.
At Curie temperature, ferromagnetic substance becomes: .
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paramagnetic
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diamagnetic
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ferromagnetic
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more ferromagnetic
Explanation
At Curie temperature, ferromagnetic substance becomes Paramagnetic.
Which of the following statement is correct for diamagnetic materials?
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$$ \mu_r < 1 $$
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$$ x $$ is negative and low
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$$ x $$ does not depend on temperature
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All of above
Explanation
The susceptibility (x) has a low negative value.
Susceptibility is independent of temperature.
The relative permeability is slightly less than one.
When placed in a non uniform magnetic field they have a tendency to move.
Which of the following statements is false?
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The direction of magnitude of magnetic field line is from $$N$$ to $$S$$
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In the region where the magnetic field lines are at a close distance from each other, there will be a strong magnetic field.
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The magnetic field lines from close loops.
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The magnetic field lines can cross each other.
Explanation
D. The magnetic field lines can cross each other.
If the magnetic field lines cross each other, it would mean that magnetic field has two directions at that point, which is not possible. Hence, magnetic field lines can cross each other.
Which of the following action will not make a magnet loose its magnetic properties
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Drop a magnet from height
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Hammer a magnet
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Pass Electric current from a current
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Heat a magnet
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