Physics - Magnetostatics
Exam Duration: 45 Mins Total Questions : 30
By magnetic screening we mean to cut out magnetic fields a small region. The material used for this purpose should be
- (a)
ferromagnetic
- (b)
antiferromagnetic
- (c)
paramagnetic
- (d)
diamagnetic
Angle of dip is maximum at
- (a)
poles
- (b)
equator
- (c)
latitude 45°
- (d)
latitude 60°
Choose the INCORRECT statement
- (a)
The ratio of magnetic induction to the intensity of the magnetising filed is called permeability
- (b)
The ratio of the intensity of magnetisation to the intensity of the magnetising field is called susceptibility
- (c)
Magnetic elements of the earth are iron, cobalt and nickel
- (d)
A magnet of pole strength 0.2 ampere-metre when cut into two pieces of equal length has the same pole strength
The needle of a dip circle will be vertical if the plane of the dip circle is
- (a)
perpendicular to the magnetic meridian
- (b)
parallel to the magnetic meridian
- (c)
in the magnetic meridian
- (d)
horizontal
The moment of a magnet is 3 ampere-metre2. It is cut into two pieces such that the length of one piece is double the length of the other. The moments of these pieces are in the ratio of
- (a)
1:2
- (b)
2:1
- (c)
1:3
- (d)
1:1
In a dip circle the plane of oscillation of the needle is adjusted in such a way that it lies
- (a)
perpendicular to the magnetic meridian
- (b)
in the magnetic meridian
- (c)
45° to the magnetic meridian
- (d)
parallel to the magnetic moment
The earth's magnetic field always has a vertical component except at
- (a)
magnetic equator
- (b)
magnetic poles
- (c)
geographic north pole
- (d)
latitude
At magnetic poles, the angle of dip is
- (a)
45°
- (b)
30°
- (c)
zero
- (d)
90°
The ratio of intensity of magnetisation and magnetising field is called
- (a)
permeability
- (b)
magnetic induction
- (c)
magnetic intensity
- (d)
magnetic susceptibility
A small pellet with a mass of 0.5 mg is fired horizontally from a gun that imparts to it a velocity of 100 ms-1. The pellet carries a charge of \(+5\mu C\). Magnetic field B is required to cancel the Earth's gravitational force on the pellet. The value of B is
- (a)
9.80 mT
- (b)
4.90 mT
- (c)
29.40 mT
- (d)
2.45 mT
In a certain Cartesian frame the velocity of an electron is \(\overrightarrow { \vartheta } =(2.5\hat { k } )\times { 10 }^{ 7 }{ ms }^{ -1 }\) and it experiences a force \(\overrightarrow { F } =(4.0\hat { i } +3.0\hat { j } )\times { 10 }^{ -13 }N\) due to the presence of a uniform magnetic field. When the velocity is redirected and becomes \(\overrightarrow { \vartheta } =(1.5\hat { i } -2.0\hat { j } )\times { 10 }^{ 7 }{ ms }^{ -1 }\), the magnetic force on the electron is zero. The component of magnetic induction vector \(\overrightarrow { B } \) is
- (a)
\(\overrightarrow { B } =(0.100\hat { i } -0.075\hat { j } )T\)
- (b)
\(\overrightarrow { B } =(-0.075\hat { i } +0.100\hat { j } )T\)
- (c)
\(\overrightarrow { B } =(-1.00\hat { i } +0.075\hat { i } )T\)
- (d)
\(\overrightarrow { B } =(0.075\hat { i } -0.100\hat { j } )T\)
A plot of the magnetic induction B versus the magnetic intensity shows that
- (a)
it rises rapidly within a small range of H values and then reaches a plateau, called saturation
- (b)
it continues to rise within a large range of H values and then reaches saturation
- (c)
it decreases rapidly within large range of H values and then reaches saturation
- (d)
it continues to rise with H
Hysteresis occurs in
- (a)
ferromagnetic material
- (b)
dielectric material
- (c)
elastic material
- (d)
ALL OF THE ABOVE
The magnetic compass is not useful for navigation near the magnetic poles.Since
- (a)
R =0
- (b)
V =0
- (c)
H =0
- (d)
\(\theta \) =0º
Agonic lines are
- (a)
zero declination
- (b)
equal declination
- (c)
zero dip
- (d)
equal dip
A circular coil of 100 turns has an effective radius of 0.05 and current of 0.1A. How much work is done to turn it through 180° in a uniform field of 1.5W/m2 if the plane of the coil is initially perpendicular to the magnetic field?
- (a)
0.5523 J
- (b)
0.3255 J
- (c)
0.2355 J
- (d)
0.5235 J
A vibration magnetometer consists of two identical bar magnets placed one over the other, such that they are mutually perpendicular and bisect each other. The time period of combination is 4 second. If one of the magnets is removed, find the period of other?
- (a)
5s
- (b)
3.36 s
- (c)
4.36 s
- (d)
5.36 s
A magnet oscillates in the earth's field with a time period T. It its mass is quadrupled, then its new time period will be
- (a)
4T
- (b)
2T
- (c)
T/2
- (d)
unaffected but motion is not SHM
A bar magnet of magnetic moment M is kept in a uniform magnetic field of the strength B, making an angle \(\theta \) with its direction. The torque acting on it is
- (a)
\(MBcos\theta \)
- (b)
MB
- (c)
\(MB(1-cos\theta )\)
- (d)
\(MBsin\theta \)
Rate of change of torque \(\tau \) with deflection \(\theta \) is maximum for a magnet suspended freely in a uniform magnetic field of induction B, when
- (a)
\(\theta =0º\)
- (b)
\(\theta =45º\)
- (c)
\(\theta =60º\)
- (d)
\(\theta =90º\)
To shield an instrument from the external magnetic field, it is placed inside a cabin made from
- (a)
wood
- (b)
ebonite
- (c)
iron
- (d)
diamagnetic substance
The vertical component of the earth's magnetic field is zero at a place where the angle of dip is
- (a)
\(0º\)
- (b)
45º
- (c)
60º
- (d)
90º
Which of the following substances has negative permeability and very large value of susceptibility?
- (a)
Ferromagnetic
- (b)
Paramagnetic
- (c)
Diamagnetic
- (d)
NONE OF THE ABOVE
A certain amount of current when flowing in a properly set tangent galvanometer produces a deflection of \(45º\). If the current be reduced by a factor of \(\sqrt { 3 } \), the deflection would
- (a)
decrease by \(30º\)
- (b)
decrease by \(15º\)
- (c)
increase by \(15º\)
- (d)
increase by \(30º\)
A circular loop of radius 0.0157 m carries a current of 2.0 A. The magnetic field at the centre of the loop is \(\left[ { \mu }_{ 0 }=4\pi \times { 10 }^{ -7 }\quad weber/amp-m \right] \)
- (a)
\(1.57\times { 10 }^{ -5 }weber/{ m }^{ 2 }\)
- (b)
\(8.0\times { 10 }^{ -5 }weber/{ m }^{ 2 }\)
- (c)
\(2.0\times { 10 }^{ -5 }weber/{ m }^{ 2 }\)
- (d)
\(3.14\times { 10 }^{ -5 }weber/{ m }^{ 2 }\)
At a certain place, the horizontal component of the earth's magnetic field is B0 and the angle of dip is \(45º\). The total intensity of the field at that place will be
- (a)
B0
- (b)
\(\sqrt { 2 } \) B0
- (c)
2B0
- (d)
\({ B }_{ 0 }^{ 2 }\)
Imaginary lines joining points of equal declination are called
- (a)
isoclinic
- (b)
Isogonic
- (c)
isodynamic
- (d)
NONE OF THESE
If a diamagnetic substance is brought near north or south pole of a bar magnet, it is
- (a)
attracted by the poles
- (b)
repelled by the poles
- (c)
repelled by north pole and attracted by south pole
- (d)
attracted by north pole and repelled by south pole