Physics - Magnetostatics
Exam Duration: 45 Mins Total Questions : 30
Choose the INCORRECT statement
- (a)
The vertical plane passing through the magnet axis of a freely suspended magnet is called magnetic meridian
- (b)
The strength of magnetic field is measured by dip circle
- (c)
The magnetic potential at any point on the equatorial line of a magnet is zero
- (d)
The ratio of intensities of magnetic fields due to a short magnet in tan A and tan B positions is 2:1
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
The neutral point in a magnetic field is a point at which
- (a)
the field due to the magnet is zero
- (b)
the field due to the magnet and the horizontal intensity of the earth's magnetic field balance each other.
- (c)
the magnetic lines of force from north pole balance those from south pole.
- (d)
the magnetic lines of force do not exist
A sphere with a magnetic dipole of moment \(\mu \) and a moment of inertia I about its diameter is placed in a uniform magnetic field of induction B. It is capable of oscillating freely about its diameter. For small oscillations, the sphere will experience restoring force per unit mass unit displacement equal to
- (a)
\(\sqrt { \frac { I }{ \mu B } } \)
- (b)
\(\sqrt { \frac { \mu B }{ I } } \)
- (c)
\(\frac { \mu B }{ I } \)
- (d)
\(\frac { \mu }{ IB } \)
When a dip circle is placed in the magnetic meridiam, the needle will make with the horizontal.
- (a)
an angle less than the dip at that place
- (b)
an angle greater than the dip at that place
- (c)
an angle equal to the dip at that place
- (d)
an angle equal to zero degree
Choose the INCORRECT statement
- (a)
The value of dip at the magnetic equator is zero degree.
- (b)
The earth's magnetism is proved by the formation of null points in the field around a bar magnet.
- (c)
Tangent law is applicable to the case of the deflection magnetometer only when the magnetometer is set in tan A and tan B positions.
- (d)
Isoclinic lines are the lines joining places of zero dip.
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
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 cosmic-ray proton in interstellar space has an energy of 10 MeV and executes a circular orbit with a radius equal to that of Mercury's orbit around the Sun \((5.8\times { 10 }^{ 10 }m)\).The galactic magnetic field in that region of space is
- (a)
\(7.8\times { 10 }^{ -12 }T\)
- (b)
\(15.6\times { 10 }^{ -12 }T\)
- (c)
\(7.8\times { 10 }^{ 12 }T\)
- (d)
\(3.9\times { 10 }^{ -12 }T\)
A metal ball with a mass of 100 g is swung with an angular speed of \(40\pi \quad rad/s\) in a horizontal circle at the end of a taut string in the presence of a uniform vertical magnetic field of 100 G. The amount of positive charge q that must be placed on the ball to double the tension in the string is
- (a)
326 C
- (b)
1260 C
- (c)
630 C
- (d)
3780 C
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
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 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
Unit of pole strength is
- (a)
Am
- (b)
Am-2
- (c)
Am-1
- (d)
Am2
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 magnet of the magnetic moment M is rotated through \(360º\) in a magnetic field H; the work done will be
- (a)
MH
- (b)
2MH
- (c)
4MH
- (d)
Zero
A magnetic needle suspended by a silk thread is vibrating in the earth's magnetic field. If the temperature of the needle is increased by \(700ºC\), then
- (a)
the time period increases
- (b)
the time period decreases
- (c)
the time period remains unchanged
- (d)
the needle stops vibrating
Unit of magnetic moment is
- (a)
Am-2
- (b)
NA-1m-1
- (c)
Nm
- (d)
Am2
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
At a neutral point
- (a)
field of magnet is zero
- (b)
field of the earth is zero
- (c)
field of magnet is perpendicular to field of the earth
- (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 \(30º\)
Two tangent galvanometers having coils of the same radius are connected in series. A current flowing in them produces deflections of \(60º\) and \(45º\) respectively. The ratio of the number of turns in the coils is
- (a)
4/3
- (b)
\((\sqrt { 3 } +1)/1\)
- (c)
\((\sqrt { 3 } +1)/(\sqrt { 3 } -1)\)
- (d)
\(\sqrt { 3 } /1\)
The meniscus of a liquid contained in one of the limbs of a narrow U-tube is held in an electromagnet with the meniscus in line with the field. The liquid is seen to rise. This indicates that the liquid is
- (a)
ferromagnetic
- (b)
paramagnetic
- (c)
diamagnetic
- (d)
non-magnetic
A vibration magnetometer is placed at the south pole, then the time period will be
- (a)
zero
- (b)
infinity
- (c)
same as at equator
- (d)
same as at any other place on the earth
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