Class 12 Physics
Chapter 4&5
(Unit -3)
• Moving charges and magnetism
• Magnetism and matter
• 20 Assertion and Reason
Type questions
• Solution with explanation
• Directions. In the following questions, statement
of assertion is followed by a statement of
reason. While answering a question, you are
required to choose the correct one out of the
given four responses and mark it as :-
• A, if both assertion and reason are true and
reason is the correct explanation of the
assertion.
• B, if both assertion and reason are true but
reason is not correct explanation of the
assertion.
• C, if assertion is true, but reason is false.
• D, if both assertion and reason are false.
1) Assertion : If the direction of velocity of
charge is parallel to the applied magnetic
field then the force experienced by moving
charge will be maximum.
Reason : The force on moving charge is
independent of the direction of applied
magnetic field.
1) A. 2) B
3) C. 4) D
2) Assertion : Magnetic field lines form
closed loop.
Reason : Moving charge or current
produce a magnetic field .
1. A
2. B
3. C
4. D
3) Assertion: If an electron and proton
enter perpendicular to a magnetic field
with equal momentum, then the paths of
both of them will be equally curved.
Reason : Since they have same
momentum, orbital radius will be same.
1) A
2) B
3) C
4) D
4) Assertion : The energy of a charged
particle does not change, when it moves
inside the magnetic field.
Reason : It is because, force on the
charged particle due to the magnetic
field acts perpendicular to its path.
1) A
2) B
3) C
4) D
5) Assertion : The coils of spring come
close to each other, when current is passed
through it.
Reason : It is because, the coils of a
spring carry current in the same direction
and hence attract each other.
1) A 2) B
3) C 4) D
6) Assertion : If the current in a solenoid
is reversed in direction while keeping the
same magnitude, the magnetic field energy
stored in the solenoid decreases.
Reason : The magnetic field energy
density is proportional to the square of
magnetic field.
1) A. 2) B
3) C. 4) D
7) Assertion : The range of an ammeter
can be both increased or decreased.
Reason: The required shunt resistance
can be calculated by using the relation,
R = G S/ G + S
1) A
2) B
3) C
4) D
8) Assertion: The range of a
voltmeter can be both increased or
decreased.
Reason : The required resistance
can be calculated by using the relation,
R = V / Ig – G
1) A. 2) B
3) C. 4) D
9) Assertion : When a bar magnet is cut
into two equal pieces transverse to its length,
the dipole moment of each piece is one half of
that of the magnet.
Reason : The pole strength if the each piece
remains the same. As the each piece possess
half the length of the magnet, the dipole
moment of a piece also becomes one half of
that of the magnet.
1) A. 2) B
3) C. 4) D
10) Assertion : Both A m^2 and J
T^-1 are the units of magnetic dipole
moment.
Reason: Both units are equivalent
to each other.
1) A
2) B
3) C
4) D
11) Assertion : An atom behaves as a
magnetic dipole.
Reason : It is because, an atom contains
equal positive and negative charges.
1) A 2) B
3) C 4) D
12) Assertion : The direction of magnetic
field due to a bar magnet at a point on its
axial line or equitorial line is same as that
of its magnetic dipole vector.
Reason : It is because, the direction of
magnetic field due to a bar magnet is always
along the magnetic dipole moment vector
1) A. 2) B
3) C. 4) D
13) Assertion : The potential energy of a
magnetic dipole is maximum, when it is
oriented anti parallel to the direction of the
magnetic field.
Reason: Because, work done is maximum,
when the magnet lying along the direction of
the field is turned so as to make it antiparallel
to the direction of the magnetic field.
1) A. 2) B
3) C. 4) D
14) Assertion : The true geographic
north direction is found by using a compass
needle.
Reason : The magnetic meridian of the
earth is along the axis of rotation of the
earth.
1) A
2) B
3) C
4) D
15) Assertion : Magnetic Induction may
be measured as T, N/mA, or J /A m^2.
Reason : All the three are equivalent.
1) A
2) B
3) C
4) D
16) Assertion : We cannot think of
magnetic field configuration with three
poles.
Reason: A bar magnet does exert a
torque on itself due to its own field.
1) A
2) B
3) C
4) D
17) Assertion : The magnetic field at
the ends of a very long current carrying
solenoid is half of that at the centre.
Reason:If the solenoid is sufficiently
long, the field within it is uniform.
1) A
2) B
3) C
4) D
18) Assertion:If two long wires,
hanging freely are connected to a
battery in series, they come closer to
each other.
Reason:Force of attraction acts
between the two wires carrying current.
1) A
2) B
3) C
4) D
19) Assertion :Free electron always keep on
moving in a conductor even then no magnetic
force act on them in magnetic field unless a
current is passed through it.
Reasons : The average velocity of free
electron is zero.
1) A
2) B
3) C
4) D
20) Assertion :Magnetic moment of
an atom is due to both, the orbital
motion and spin motion of every
electron
Reason :A charged particle produces
a magnetic field.
1) A
2) B
3) C
4) D
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