Knowledge Academy - Class 12th Physics - Chapter
4: Moving Charges and Magnetism
Multiple Choice Questions
(i) A moving charge experiences maximum force in a magnetic
field when:
(A) The velocity of the charge is parallel to the magnetic field.
(B) The velocity of the charge is perpendicular to the magnetic field.
(C) The velocity of the charge is at a 45° angle to the magnetic field.
(D) The charge is at rest.
Answer: (B) The velocity of the charge is perpendicular to the
magnetic field.
(ii) A proton and an alpha particle enter a uniform magnetic field
with the same velocity and direction. The ratio of the radii of
their circular paths is:
(A) 1:1
(B) 1:2
(C) 1:4
(D) 2:1
Answer: (B) 1:2
(iii) The magnetic field inside a long straight solenoid is:
(A) Non-uniform and parallel to the axis.
(B) Uniform and parallel to the axis.
(C) Uniform and perpendicular to the axis.
(D) Zero.
Answer: (B) Uniform and parallel to the axis.
(iv) Two current-carrying conductors flowing in the same
direction will:
(A) Repel each other.
(B) Attract each other.
(C) Exert no force on each other.
(D) Become neutral.
Answer: (B) Attract each other.
(v) The direction of the magnetic field produced by a straight
current-carrying conductor can be determined by:
(A) Fleming's right-hand rule.
(B) Fleming's left-hand rule.
(C) Right-hand thumb rule.
(D) Ampere's rule.
Answer: (C) Right-hand thumb rule.
Fill in the Blanks
(i) The resistance of an ideal ammeter is ________.
Answer: zero
(ii) The resistance of an ideal voltmeter is ________.
Answer: infinite
(iii) The force acting on a moving charge in a magnetic field is
called the ________ force.
Answer: Lorentz
(iv) If a charged particle moves in a uniform magnetic field in the
direction of the field, the force acting on it will be ________.
Answer: zero
(v) The magnetic field lines are always ________ loops.
Answer: closed
State whether the following statements are True or False:
(i) Increasing the number of turns in a coil increases the
sensitivity of a voltmeter.
Answer: True. A higher number of turns in the coil leads to a larger
deflection for the same voltage, thus increasing sensitivity.
(ii) Increasing the number of turns in a coil increases the
sensitivity of a galvanometer.
Answer: True. The sensitivity of a galvanometer is directly
proportional to the number of turns in the coil.
(iii) The magnetic field produced by a long straight current-
carrying wire is similar to that of a bar magnet.
Answer: False. The magnetic field lines of a long straight wire are
concentric circles around the wire, while a bar magnet has field
lines that originate from the North Pole and end at the South Pole.
(iv) A current-carrying planar loop behaves like a magnetic
dipole.
Answer: True. A current loop creates a magnetic field similar to that
of a magnetic dipole, with a magnetic moment equal to IA, where I is
the current and A is the area of the loop.
(v) Ampere's circuital law is applicable only to those currents
that change with time.
Answer: False. Ampere's circuital law is valid for steady currents
and does not require the current to be time-varying. The law for
time-varying currents includes Maxwell's correction and is known as
the Ampere-Maxwell law.
