CBSE Questions for Class 12 Medical Physics Magnetism And Matter Quiz 7 - MCQExams.com

Super conductors are
  • most exotic diamagnetic materials
  • ferromagnetic material with low resistivity
  • Paramagnetic materials at high temperature
  • none of these
A rectangle with its dimensions is as shown. A Magnetic mono pole of pole strength 'm' is placed at the point 'A' and another pole of pole strength '5m' is placed at the point 'B'. The magnetic force acting between them is 'F'. If magnetic pole at the point 'B' is moved to the point 'C', Find final magnetic force acting between them.

102887.jpg
  • $$ \dfrac{F}{10} $$
  • $$ \dfrac{F}{17} $$
  • $$ \dfrac{F}{20} $$
  • $$ F $$
State whether true or false.
Magnetic lines of force do not intersect.
  • True
  • False
The earth's magnetic field at the equator is approximately $$0.4 G$$. The earth's dipole moment is :
$$(R_e = 6.4 \times 10^6 m)$$
  • $$4 \times 10^2 Am^2$$
  • $$1.05 \times 10^{23} Am^2$$
  • $$4 \times 10^{-5} Am^2$$
  • $$1.05 \times 10^{-20} Am^2$$
State whether true or false.
A magnetic field is a region around a magnet where magnetic lines of force act.
  • True
  • False
Choose the correct statement from the following:
  • Magnetic lines of force never intersect.
  • Magnetic lines of force emanate from north pole.
  • Magnetic lines of force travel in straight lines.
  • Magnetic lines of force are curved lines.
The correct I-H curve for a paramagnetic material is represented by, figure
  • straight line
  • closed loop
  • none
A uniform magnetic field parallel to the plane of 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 figure.
If a diamagnetic substance is brought near the north or the south pole of a bar magnet, it is
  • attracted by both the poles
  • repelled by both the poles
  • repelled by the north pole and attracted by the south pole
  • attracted by the north pole and repelled by the south pole
The variation of magnetic susceptibility ($$\chi$$) with temperature for a diamagnetic substance is best represented by figure :
The vertical component of Earth's magnetic field is zero at, or the Earth's magnetic field always has a vertical component except at the
  • magnetic poles
  • geographic poles
  • every place
  • magnetic equator
A bar magnet $$30\ cm$$ long is placed in the magnetic meridian with its north pole pointing south. The neutral point is observed at a distance of $$30\ cm$$ from its one end. Calculate the pole strength of the magnet. Given horizontal component of earth's field $$= 0.34\ G.$$
  • 4.3 Am
  • 5.2 Am
  • 6.9 Am
  • 8.6 Am
The total intensity of the earth's magnetic field at equator is $$5$$ units. What is its value at the poles?
  • $$5$$
  • $$4$$
  • $$3$$
  • $$2$$
A copper rod is suspended a non-homogeneous magnetic field region. The rod when in equilibrium will align itself:
  • in the region where magnetic field is strongest
  • in the region where magnetic field is weakest and parallel to direction of magnetic field there
  • in the direction in which it was originally suspended
  • in the region where magnetic field is weakest and perpendicular to the direction of magnetic field there
The earth's magnetic field may be considered to be due to a short magnet placed at the centre of earth and oriented along magnetic south-north direction. The ratio of magnitude of magnetic field on earth's surface at magnetic equator and that at magnetic poles is:
  • $$1 : 2$$
  • $$2 : 1$$
  • $$1 : 4$$
  • $$4 : 1$$
If a piece of soft iron is placed inside the coil $$n$$ number of turns and current is passed in the coil from a battery, what name is then given to the device so obtained ?
  • spectrometer
  • gravitometer
  • barometer
  • electromagnet
The value of earth's magnetic field can be
  • $$0.5G$$
  • $$5G$$
  • $$10G$$
  • $$50G$$
Magnetic susceptibility $$\chi$$ of a paramagnetic material changes with absolute temperature $$T$$ as  
  • $$\chi\propto T^{-1}$$
  • $$\chi=constant$$
  • $$\chi\propto e^{T}$$
  • $$\chi\propto T$$
Soft iron is used for the construction of electromagnets because for iron 
  • the area of hysteresis loops is more.
  • coersive force is high.
  • retentivity is high.
  • magnetic saturation limits is high and coercivity is low.
Relative permittivity and permeability of a material are $$\varepsilon_1$$ and $$\mu_1$$ respectively. Which of the following values of these quantities are allowed for a diamagnetic material?
  • $$\varepsilon_r = 1.5, \mu_r = 0.5$$
  • $$\varepsilon_r = 0.5, \mu_r = 0.5$$
  • $$\varepsilon_r = 1.5, \mu_r = 1.5$$
  • $$\varepsilon_r = 0.5, \mu_r = 1.5$$
The value of magnetic susceptibility for para-magnetic substance is  
  • infinity
  • low positive
  • low negative
  • zero
A long straight wire carries a current along the Z-axis. One can find two points in the X-Y plane such that :
  • the magnetic fields are equal
  • the direction of the magnetic fields are the same
  • the magnitude of the magnetic fields are equal
  • the field at one point is opposite to that at the other point
What is $$\mu_{max}$$ equal to?
146491_642ae9daec8c47bbad348c27e7ffbef0.png
  • $$\mu_{max}\approx1.0\times10^4$$
  • $$\mu_{max}\approx2.0\times10^4$$
  • $$\mu_{max}\approx1.0\times10^3$$
  • $$\mu_{max}\approx2.0\times10^3$$
Name the device that uses an electromagnet
  • Electric bell
  • Barometer
  • Lactometer
  • All the above
The __________ in a magnetic field is called magnetic lines of force.
  • Open curves
  • Closed curves
  • Circles
  • Polygons
A magnetic needle suspended horizontally by an unspun silk fibre oscillates in the horizontal plane, because of the restoring force originating mainly from
  • the torsion of the silk fibre
  • the horizontal component of earth's magnetic field
  • the force of gravity
  • all of the above
The B-H curve (i) and (ii) shown in the given figure is associated with
204739_cc3c397d8f4b41269b736e4b059e5c93.png
  • (i) diamagnetic and (ii) paramagnetic substance
  • (i) paramagnetic and (ii) ferromagnetic substance
  • (i) soft iron (ii) steel
  • (i) steel and (ii) soft iron
The magnitude of the induced current in a closed coil increases with the increase in the strength of a magnet. The statement is
  • true
  • false
  • ambiguous
  • data insufficient 
Which part  has maximum attraction in a magnet ?
  • In the centre
  • On the sides
  • On the poles
  • On the surface
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 $${700}^{o}$$C, then
  • time period decreases
  • time period increases
  • time period remains unchanged
  • the needle stops vibrating
When will the coil come to rest ?
  • when its plane becomes parallel to the magnetic field.
  • when its plane becomes normal to the magnetic field.
  • when its plane becomes acute angled to the magnetic field.
  • when its plane becomes obtuse angled to the magnetic field.
State whether true or false:
A permanent magnet is used in an electric bell.     
  • True
  • False
Of the following figure, the lines of magnetic induction due to a magnet $$SN$$, are given by :

205323_8b3981fac8984a5ca95b5cd6114a08a0.png
  • $$1$$
  • $$2$$
  • $$3$$
  • $$4$$
A frog can be levitated 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 :
  • paramagnetic
  • diamagnetic
  • ferromagnetic
  • antiferromagnetic
 Magnetic field represented by parallel and equidistant field lines are:
  • Non-uniform
  • Zero
  • Uniform
  • None of these
Needles $${N}_{1},{N}_{2},{N}_{3}$$ are made of a ferromagnetic, a paramagnetic and a diamagnetic substance respectively. A magnet when brought close to them will:
  • attract $${N}_{1}$$ and $${N}_{2}$$ strongly but repel $${N}_{3}$$
  • attract $${N}_{1}$$ strongly, $${N}_{2}$$ weakly and repel $${N}_{3}$$ weakly
  • attract $${N}_{1}$$ strongly, but repel $${N}_{2}$$ and $${N}_{3}$$ weakly
  • attract all three of them
On the basis of following features identify the correct option 
I. They always start from north pole and end at the south pole of the magnet outside the magnet.
II. They never intersect each other.
  • Electric lines of force
  • Magnetic lines of force
  • Both (1) and (2)
  • Neither (1) nor (2)
Magnetic lines of force determines: 
  • The shape of the magnetic field
  • Only the direction of the magnetic field
  • Only the relative strength of the magnetic field
  • Both the direction and the relative strength of the magnetic field
Magnetic field lines
  • Cannot interest at all
  • Intersect at infinity
  • Intersect within the magnet
  • Intersect at the neutral points
The Earths magnetic field at a point P near the equator has only a horizontal component. A horizontal over head high tension wire above this point carries a current such that it completely nullifies this horizontal component at P. The direction of the current in the wire is most likely
  • north to south.
  • south to north.
  • east to west.
  • west to east.
When the atomic magnetic moments are randomly oriented in a solid its magnetic behavior is termed as
  • semi-magnetic.
  • anti-ferromagnetic.
  • paramagnetic.
  • poly crystalline.
Magnetic lines of force inside a bar magnet
  • Are from north pole to south pole of the magnet
  • Do not exist
  • Depend upon the area of cross section of the bar magnet
  • Are from south pole to north pole of the magnet
When the bars of bismuth are placed between the magnetic poles they set their length
  • Perpendicular to the lines of force
  • Along the lines of force
  • Neither perpendicular nor along the lines of force
  • In any direction
Magnetic lines of force
  • are mere directions.
  • have no physical reality.
  • can be used to indicate the direction of the magnetic field at point.
  • all the above are correct.
Which of the following statements is INCORRECT?
  • Electric current is a scalar quantity.
  • Electric lines of force are closed curves.
  • Magnetic lines of induction are closed curves.
  • Changing magnetic field induces an electric current in a coil.
Magnetic lines do not intersect one-another because
  • They are at a distance
  • They are in the same direction
  • They are parallel to another
  • At the point intersection there will be two direction of the magnetic force which is impossible
The direction of magnetic field line in case of a bar magnet at point A & B are
321672_a7a880dc69934e97bb20972ea930298b.png
  • $$\leftarrow$$ at A and $$\rightarrow$$ at B
  • $$\leftarrow$$ at A and $$\leftarrow$$ at B
  • $$\rightarrow$$ at A and $$\rightarrow$$ at B
  • $$\rightarrow$$ at A and $$\leftarrow$$ at B
Which of the following shows that the earth behaves as a magnet ?
  • Repulsion between like poles
  • Attraction between unlike poles
  • Existence of null points in the magnetic field of a bar magnet
  • Non-existence of monopoles
Which of the following figures represents the magnetic lines of force due to an isolated north pole?
A bar magnet has been cut equally lengthwise and widthwise to give four equal pieces. The pole strength of each piece as compared to the pole strength of original bar magnet is :
  • Same
  • $$\displaystyle \frac{1}{8}$$
  • $$\displaystyle \frac{1}{4}$$
  • $$\displaystyle \frac{1}{2}$$
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