Free download in PDF CBSE Class 12 Physics Multiple Choice Questions(MCQs) with Answers. Here Gkseries provide Physics Solve Questions and Answers for CBSE Class 12 Students.
61
If a charged particle moves through a magnetic field perpendicular to it
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.
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
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: 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.
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
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.
