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Free download in PDF CBSE Class 11 Physics Multiple Choice Questions(MCQs) with Answers. Here Gkseries provide Physics Solve Questions and Answers for CBSE Class 11 Students.
61
If a charged particle moves through a magnetic field perpendicular to it
[A]
both momentum and energy of particle change.
[B]
momentum as well as energy are constant.
[C]
energy is constant but momentum changes.
[D]
momentum is constant but energy changes.
Answer: energy is constant but momentum changes.
62
Consider a wire carrying a steady current, I placed in a uniform magnetic field B perpendicular to its length. Consider the charges inside the wire. It is known that magnetic forces do not work. This implies that,
[A]
motion of charges inside the conductor is unaffected by B, since they do not absorb energy.
[B]
Some charges inside the wire move to the surface as a result of B.
[C]
if the wire moves under the influence of B, no work is done by the force.
[D]
If the wire moves under the influence of B, no work is done by the electric force on the ions, assumed fixed within the wire.
Answer: Some charges inside the wire move to the surface as a result of B.
63
A cubical region of space is filled with some uniform electric and magnetic fields. An electron enters the cube across one of its faces with velocity v and a positron enters via opposite face with velocity -v. At this instant,
[A]
the electric forces on both the particles cause identical accelerations.
[B]
the magnetic forces on both the particles cause equal accelerations.
[C]
Only electron gains or looses energy.
[D]
the motion of the centre of mass (CM) is determined by E alone.
Answer: the magnetic forces on both the particles cause equal accelerations.
64
A circular coil of radius 4 cm and of 20 turns carries a current of 3 amperes. It is placed in a magnetic field of intensity of 0.5 weber/m². The magnetic dipole moment of the coil is
[A]
0.15 ampere-m²
[B]
0.3 ampere-m²
[C]
0.45 ampere-m²
[D]
0.6 ampere-m²
65
In a cyclotron, a charged particle [NCERT Exemplar]
[A]
undergoes acceleration all the time.
[B]
speeds up between the dees because of the magnetic field.
[C]
speeds up in a dee.
[D]
slows down within a dee and speeds up between dees.
Answer: undergoes acceleration all the time.
66
An electron is projected with uniform velocity along the axis of a current carrying long solenoid. Which of the following is true? [NCERT Exemplar]
[A]
The electron will be accelerated along the axis.
[B]
The electron path will be circular about the axis.
[C]
The electron will experience a force at 45° to the axis and hence execute a helical path.
[D]
The electron will continue to move with uniform velocity along the axis of the solenoid
Answer: The electron will continue to move with uniform velocity along the axis of the solenoid
67
A current carrying circular loop of radius R is placed in the x-y plane with centre at the origin. Half of the loop with x > 0 is now bent so that it now lies in the y – z plane. [NCERT Exemplar]
[A]
The magnitude of magnetic moment now diminishes.
[B]
The magnetic moment does not change.
[C]
The magnitude of B at (0.0.z), z» R increases.
[D]
The magnitude of B at (0, 0, z), z » R is unchanged.
Answer: The magnitude of magnetic moment now diminishes.
68
If the magnetising field on a ferromagnetic material is increased, its permeability.
[A]
is decreased
[B]
is increased
[C]
is unaffected
[D]
may be increased or decreased.
69
Lines of force, due to earth’s horizontal magnetic field, are
[A]
parallel and straight
[B]
concentric circles
[C]
curved lines
[D]
elliptical
Answer: parallel and straight
70
Angle of dip is 90° at
[A]
poles.
[B]
tropic of cancer.
[C]
equator.
[D]
both at equator and poles.
71
Curie law xT = constant, relating magnetic susceptibility (x) and absolute temperature (T) of magnetic substance is obeyed by
[A]
all magnetic substances.
[B]
paramagnetic substances.
[C]
diamagnetic substances.
[D]
ferromagnetic substances.
Answer: paramagnetic substances.
72
The material suitable for making electromagnets should have
[A]
high retentivity and high coercivity.
[B]
low retentivity and low coercivity.
[C]
high retentivity and low coercivity.
[D]
low retentivity and high coercivity.
Answer: high retentivity and low coercivity.
73
Curie temperature is the temperature above which
[A]
a ferromagnetic material becomes paramagnetic.
[B]
a ferromagnetic material becomes diamagnetic.
[C]
a paramagnetic material becomes diamagnetic.
[D]
a paramagnetic material becomes ferromagnetic.
Answer: a ferromagnetic material becomes paramagnetic.
74
Three needles N1 N2 and N3 are made of a ferromagnetic, a paramagnetic and a diamagnetic substance respectively. A magnet, when brought close to them, will
[A]
attract N1 strongly, but repel N2 and N3 weakly.
[B]
attract all three of them.
[C]
attract N1 and N2 strongly but repel N3.
[D]
attract N1 strongly, N2 weakly and repel N3 weakly.
Answer: attract N1 strongly, N2 weakly and repel N3 weakly.
75
A magnetic needle is kept in a non-uniform magnetic field. It experiences
[A]
a torque but not a force.
[B]
neither a force nor a torque.
[C]
a force and a torque.
[D]
a force but not a torque.
Answer: a force and a torque.
76
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
[A]
is always zero.
[B]
can be zero at specific points.
[C]
cannot be positive or negative.
[D]
is not bounded.
Answer: can be zero at specific points.
77
Essential difference between electrostatic shielding by a conducting shell and magne-tostatic shielding is due to
[A]
electrostatic field lines cannot end on ’ charges and conductors do not have free charges.
[B]
lines of B can also end but conductors cannot end them.
[C]
lines of B cannot end. on any material and perfect shielding is not possible.
[D]
shells of high permeability materials cannot be used to divert lines of B from the interior region.
Answer: lines of B cannot end. on any material and perfect shielding is not possible.
78
A long solenoid has 1000 turns per metre and carries a current of 1 A. It has a soft iron core of μr = 1000. The core is heated beyond the Curie temperature, Tc .
[A]
The H field in the solenoid is (nearly) unchanged but the B field decreases drastically.
[B]
The H and B fields in the solenoid are nearly unchanged.
[C]
The magnetisation in the core reverses direction.
[D]
The magnetisation in the core does not diminishes.
Answer: The H field in the solenoid is (nearly) unchanged but the B field decreases drastically.
79
The primary origin(s) of magnetism lies in
[A]
Pauli exclusion principle.
[B]
polar nature of molecules.
[C]
intrinsic spin of electron.
[D]
None of these.
Answer: polar nature of molecules.
80
S is the surface of a lump of magnetic material.
[A]
Lines of H cannot all be continuous across S.
[B]
Lines of H are necessarily continuous across S.
[C]
Some lines of B must be discontinuous across S.
[D]
Lines of B are not necessarily continuous across S.
Answer: Lines of H cannot all be continuous across S.
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