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question_answer1)
Directions : (1-5) |
Element of the Earths Magnetic field |
The earth's magnetic field at a point on its suface is usually characterised by three quantities : [a] declination [b] inclination or dip and [c] horizontal component of the field. These are knwon as the elements of the earth's magnetic field. At a place, angle between geographic meridian and magnetic meridian is defined as magnetic declination, whereas angle made by the earth's magnetic field with the horizontal in magnetic meridian is known as magnetic dip. |
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In a certain place, the horizontal component of magnetic field is \[\frac{1}{\sqrt{3}}\] times the vertical component. The angle of dip at this place is
A)
zero done
clear
B)
\[\pi /3\] done
clear
C)
\[\pi /2\] done
clear
D)
\[\pi /6\] done
clear
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question_answer2)
The angle betwen the true geographic north and the north shown by a compass needle is called as
A)
inclination done
clear
B)
magnetic declination done
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C)
angle of meridian done
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D)
magnetic pole. done
clear
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question_answer3)
The angles of dip at the poles and the equator respectively are
A)
\[30{}^\circ ,\text{ }60{}^\circ \] done
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B)
\[0{}^\circ ,\text{ }90{}^\circ \] done
clear
C)
\[45{}^\circ ,\text{ }90{}^\circ \] done
clear
D)
\[90{}^\circ ,\text{ }0{}^\circ \] done
clear
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question_answer4)
A compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole. It
A)
will become rigid showing no movement done
clear
B)
will stay in any position done
clear
C)
will stay in north-south direction only done
clear
D)
will stay in east-west direction only. done
clear
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question_answer5)
Select the correct statement from the following
A)
The magnetic dip is zero at the centre of the earth done
clear
B)
Magnetic dip decreases as we move away from the equator towards the magnetic pole done
clear
C)
Magnetic dip increases as we move away from the equator towards the magnetic pole done
clear
D)
Magnetic dip does not vary from place to place. done
clear
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question_answer6)
Directions : (6-10) |
Gausss Low for Magnetism |
By analogy to Guass's law of electrostatics, we can |
write Gauss's law of magnetism as \[\oint{\overrightarrow{B}\,.\,\overrightarrow{ds}}={{\mu }_{0}}{{m}_{inside}}\] wehre \[\oint{\overrightarrow{B}\,.\,\overrightarrow{ds}}\] is the magnetic flux and \[{{m}_{inside}}\]is the net pole strength inside the closed surface. |
We do not have an isolated magnetic pole in nature. At least none has been found to exist till date. The smallest unit of the source of magnetic field is a magnetic dipole where the net magnetic pole is zero. Hence, the net magnetic pole enclosed by any closed surface is always zero. Correspondingly, the flux of the magnetic field through any closed surface is zero. |
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Consider the two idealised 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) \[\overrightarrow{E}\] is ideally treated as a constant betwen plates and zero outside. In (ii) magnetic field is constant inside the solenoid and zero ouside. These idealised assumption, however, contradict fundamental laws as |
A)
case (i) contradicts Gauss's law for electrostatic field done
clear
B)
case (ii) contradicts Gauss's law for magnetic fields done
clear
C)
case (i) agrees with \[\oint{\overrightarrow{E}\,.\,\overrightarrow{dl}}=0\] done
clear
D)
case (ii) contradicts \[\oint{\overrightarrow{H}\,.\,\overrightarrow{dl}}={{I}_{en}}\] done
clear
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question_answer7)
The net magnetic flux through any closed surface, kept in a magnetic field is
A)
zero done
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B)
\[\frac{{{\mu }_{0}}}{4\pi }\] done
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C)
\[4\pi {{\mu }_{0}}\] done
clear
D)
\[\frac{4{{\mu }_{0}}}{\pi }\] done
clear
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question_answer8)
A closed surface S encloses a magnetic diple of magnetic moment 2ml. The magnetic flux emerging from the surface is
A)
\[{{\mu }_{0}}m\] done
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B)
zero done
clear
C)
\[4H\,{{\mu }_{0}}m\] done
clear
D)
\[\frac{2\,m}{{{\mu }_{0}}}\] done
clear
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question_answer9)
Which of the following is not a consequence of Gauss's law?
A)
The magnetic poles always exist as unlike pairs of equal strength done
clear
B)
If several magnetic lines of forces enter in a closed surface, then an equal number of lines of force must leave that surface done
clear
C)
There are abundant sources or sinks of the magnetic field inside a closed surface. done
clear
D)
Isolated magnetic poles do not exist. done
clear
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question_answer10)
The surface integral of a magnetic field over a surface
A)
is proportional to mass enclosed done
clear
B)
is proportional to charge enclosed done
clear
C)
is zero done
clear
D)
equal to its magnetic flux through that surface. done
clear
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question_answer11)
Directions : (11-15) |
Magnetisation and Magnetic Intensity |
When the atomic dipoles are aligned partially or fully, there is a net magnetic moment in the direction of the field in any small volume of the material. The actual magnetic field inside material placed in magnetic field is the sum of the applied magnetic field and the magnetic field due to magnetisation. This field is called magnetic internsity (H) |
\[H=\frac{B}{{{\mu }_{0}}}-M\] |
where M is the magnetisation of the material, \[{{\mu }_{0}}\]is the permittivity of vacuum and B is the total magnetic field. The measure that tells us how a magnetic material responds to an external field is given by a dimensionless quantity is appropriately called the magnetic susceptibility : for a certain class of magnetic materials, intensity of magnetisation is directly proportional to the magnetic intensity |
Magntisation of a sample is
A)
volume of sample per unit magnetic moment done
clear
B)
net magnetic moment per unit volume done
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C)
ratio of magnetic moment and pole strength done
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D)
ratio of pole strength to magnetic moment. done
clear
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question_answer12)
Identify the wrongly matched quantity and unit pair
A)
B)
C)
D)
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question_answer13)
A bar magnet has length 3 cm, cross-sectional area \[2\,c{{m}^{2}}\] and magnetic moment \[3\,A\,{{m}^{2}}\]. The intensity of magnetisation of bar magnet is
A)
\[2\times {{10}^{5}}\,\,A/m\] done
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B)
\[3\times {{10}^{5}}\,\,A/m\] done
clear
C)
\[4\times {{10}^{5}}\,\,A/m\] done
clear
D)
\[5\times {{10}^{5}}\,\,A/m\] done
clear
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question_answer14)
A solenoid has core of a material with relative permeability 500 and its windings carry a current of 1 A. The number of turns of the solenoid is 500 per metre. The magnetization of the material is nearly
A)
\[2\centerdot 5\times {{10}^{3}}A{{m}^{-1}}\] done
clear
B)
\[2\centerdot 5\times {{10}^{5}}A{{m}^{-1}}\] done
clear
C)
\[2\centerdot 0\times {{10}^{3}}A{{m}^{-1}}\] done
clear
D)
\[2\centerdot 0\times {{10}^{5}}A{{m}^{-1}}\] done
clear
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question_answer15)
The relative permeability of iron is 6000. Its magnetic susceptibility is
A)
5999 done
clear
B)
60001 done
clear
C)
\[6000\times {{10}^{-7}}\] done
clear
D)
\[600\times {{10}^{7}}\] done
clear
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question_answer16)
Directions : (16-20) |
Earths Magnetic field |
The magnetic field lines of the earth resemble that of a hypothetical magnetic dipole located at the centre of the earth. The axis of the dipole is presently tilted by approximately \[11\centerdot 3{}^\circ \] with respect to the axis of rotation of the earth. |
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The pole near the geographic North pole of the earth is called the North magnetic pole and the pole near the geographic South pole is called South magnetic pole. |
The strength of the earth's magnetic field varies from place to pake on the earth's surface, its value being of the order of
A)
\[{{10}^{5}}T\] done
clear
B)
\[{{10}^{-6}}\,T\] done
clear
C)
\[{{10}^{-5}}\,T\] done
clear
D)
\[{{10}^{8}}\,T\] done
clear
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question_answer17)
A bar magnet is placed North-south with its North-pole due North. The points of zero magnetic field will be in which direction from centre of magnet?
A)
North-South done
clear
B)
East-West done
clear
C)
North-East and South-West done
clear
D)
None of these. done
clear
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question_answer18)
The value of angle of dip is zero at the magnetic equator because on it
A)
V and H are equal done
clear
B)
the values of V and H zero done
clear
C)
the value of V is zero done
clear
D)
the value of H is zero. done
clear
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question_answer19)
The angle of dip at a certain place, where the horizontal and vertical components of the earth's magnetic field are equal, is
A)
\[30{}^\circ \] done
clear
B)
\[90{}^\circ \] done
clear
C)
\[60{}^\circ \] done
clear
D)
\[45{}^\circ \] done
clear
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question_answer20)
At a place, angle of dip is \[30{}^\circ \]. If horizontal component of earth's magnetic field is H. then the total intensity of magnetic field will be
A)
\[\frac{H}{2}\] done
clear
B)
\[\frac{2H}{\sqrt{3}}\] done
clear
C)
\[H\sqrt{\frac{3}{2}}\] done
clear
D)
2H done
clear
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question_answer21)
Directions : (21-25) |
Magnetic field due to a Hollow Wire |
The field of a hollow wire with constant current is homogeneous. |
Curves in the graph shown give, as ruction of radial distance r, the magnitude B of the magnetic field inside and outside four long wires a, b, c and d carrying currents that are uniformly distributed across the cross sections of the wires. Overlapping portions of the plotsare indicated by double labels. |
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Which wire has the greatest magnitude of the magnetic field on the surface?
A)
a done
clear
B)
b done
clear
C)
c done
clear
D)
d done
clear
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question_answer22)
The current density in a wire a is
A)
greater than in wire c done
clear
B)
less than in wire c done
clear
C)
equal to that in wire c done
clear
D)
not comparable to that of in wire c doc to tack of information done
clear
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question_answer23)
Which wire has the greatest radius ?
A)
a done
clear
B)
b done
clear
C)
c done
clear
D)
d done
clear
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question_answer24)
A direct current I flows along the length of an infinitely long straight thin walled pipe, then the magnetic field is
A)
uniform throughout the pipe but not zero done
clear
B)
zero only along the axis of the pipe done
clear
C)
zero at any point inside the pipe done
clear
D)
maximum at the centre and minimum at he edges. done
clear
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question_answer25)
In a coaxial, straight cable, the central conductor and the outer conductor carry equal currents in opposite direction. The magnetic field is zero
A)
outside the cable done
clear
B)
inside the inner conductor done
clear
C)
inside the outer conductor done
clear
D)
in between the two conductors. done
clear
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