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NCERT Solutions for class 12 Physics | Chapter 5 - Magnetism and Matter

(1) The magnetic lines of force inside a bar magnet:
[A] do not exist
[B] depends on area of cross-section of bar magnet
[C] are from N-pole to S-pole of the magnet
[D] are from S-pole to N-pole of the magnet.
Answer: are from S-pole to N-pole of the magnet.
(2) The magnetic field strength due to a short bar magnet directed along its axial line at a distance r is B. What is its value at the same distance along the equatorial line?
[A] B
[B] 2B
[C] B/2
[D] B/4
Answer: B/2

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(3) In a bar magnet, magnetic lines of force z :
[A] are produced only at north pole like rays of light from a bulb
[B] starts from north pole and ends at the south pole
[C] emerge in circular paths from the middle of the bar
[D] run continuously through the bar and outside
Answer: starts from north pole and ends at the south pole
(4) The relation between geometric length (L) and magnetic length (Lm) is:
[A]
[B]
[C] (a) Lm = Lg
[D] Lm = 2RY;UL Lg
Answer:
(5) The force acting per unit length of a semi circular wire of radius R carrying a current I is:
[A]
[B]
[C]
[D]
Answer:
(6) The neutral point in the magnetic field of a horizontally placed bar magnet is a point where the magnetic field due to that bar magnet is:
[A] zero
[B] more than that of earth
[C] less than that of earth
[D] equal to that of earth
Answer: equal to that of earth
(7) What is the magnetic field in the empty space enclosed by the toroidal solenoid of radius ‘R’? ,
[A] Infinity
[B]
[C]
[D] zero
Answer: zero
(8) Ferrites may be:
[A] ant. ferromagnetic
[B] ferromagnetic
[C] ferrimagnetic
[D] None of the above
Answer: ferromagnetic
(9) The magnetic field at the centre of a current carrying circular loop is B. If the radius of the loop is doubled keeping the current unchanged, the magnetic field at the centre of loop will become:
[A] B/2
[B] B/4
[C] 2B
[D] 4B
Answer: B/4
(10) A magnetic bar of M magnetic moment is placed m the field of magnetic strength B, the torque acting on it is :
[A]
[B]
[C]
[D]
Answer: C
(11) The dimensional representation of is similar to that of:
[A] frequency
[B] time
[C] distance
[D] speed
Answer: time
(12) What is the angle of dip at a place where the horizontal component of earth’s magnetic field is equal to the vertical component?
[A] 0°
[B] 30°
[C] 45°
[D] 90°
Answer: 45°
(13) S.I. unit of flux is :
[A] Ohm
[B] Weber
[C] Tesla
[D] None
Answer: Weber
(14) The dimensional representation of magnetic flux density is :
[A] [MLT-2]
[B] [MLT-2A-1]
[C] [MLT-2A-2]
[D] [MT-2A-1]
Answer: [MT-2A-1]
(15) In a moving coil galvanometer, we use a radial magnetic field so that the galvanometer scale is :
[A] exponential
[B] linear
[C] algebraic
[D] logarithmic
Answer: linear
(16) A wire of length I has a magnetic moment M. It is then bent into a semi-circular arc. The neyv magnetic moment is :
[A] M
[B] M.l.
[C] 2M/π
[D] M/π
Answer: 2M/π
(17) Which of the following is not showing the essential difference between electrostatic shielding by a conducting shell and magnetostatic shielding?
[A] Electrostatic field lines can end on charges and conductors have free charges.
[B] Magnetic field lines can end but conductors cannot end them.
[C] Lines of magentic field cannot end on any material and perfect shielding is not possible.
[D] Shells of high permeability materials can be used to divert lines of magnetic field from the interior region.
Answer: Magnetic field lines can end but conductors cannot end them.
(18) Which of the following property shows the property of ferromagnetic substances?
[A] The ferromagnetic property depends on tem-perature. ‘
[B] The ferromagnetic property does not depend on temperature.
[C] At high enough temperature ferromagnet becomes a diamagnet.
[D] At low temperature ferromagnet becomes a paramagnet.
Answer: The ferromagnetic property depends on tem-perature.
(19) Let the magnetic field on earth be modelled by that of a point magnetic dipole at the centre of earth. The angle of dip at a point on the geographical equator is
[A] always zero
[B] positive, negative or zero
[C] unbounded
[D] always negative
Answer: positive, negative or zero
(20) Which of the following is responsible for the earth’s magnetic field?
[A] Convective currents in earth’s core
[B] Diversive current in earth’s core.
[C] Rotational motion of earth.
[D] Translational motion of earth.
Answer: Convective currents in earth’s core

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