# CBSE Class 12 Physics Moving Charges and Magnetism MCQs

## Moving Charges and Magnetism Class 12 Physics MCQ

Class 12 Physics students should refer to the following multiple-choice questions with answers for Moving Charges and Magnetism in standard 12. These MCQ questions with answers for Grade 12 Physics will come in exams and help you to score good marks

### Moving Charges and Magnetism MCQ Questions Class 12 Physics with Answers

Question:  Biot-Savart law indicates that the moving electrons (velocity v) produce a magnetic field B such that
(a) B is perpendicular of
(b) B is parallel to v
(c) it obeys inverse cube law
(d) it is along the line joining the electron and point of observationt

Question: 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.
(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

Question:  An electron is projected with uniform velocity along the axis of a current carrying long solenoid. Which of the following is true?
(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

Question:  In a cyclotron, a charged particle
(a) undergoes acceleration all the time
(b) speeds up between the dees because of the magnetic field
(c) speeds up in a dees
(d) slows down within a dee and speeds up between dees

Question: If we double the radius of a coil keeping the current through it unchanged, then the magnetic field at any point at a large distance from the centre becomes approximately
(a) double
(b) three times
(c) four times
(d) one-fourth

Question:  A proton and an alpha particle both enter a region of uniform magnetic field B, moving at right angles to field B. If the radius of circular orbits for both the particles is equal and the kinetic energy acquired by proton is 1 MeV the energy acquired by the alpha particle will be:
(a) 0.5 MeV
(b) 1.5 MeV
(c) 1 MeV
(d) 4 MeV

Question: A charged particle moving in a uniform magnetic field and losses 4% of its kinetic energy. The radius of curvature of its path changes by
(a) 2%
(b) 4%
(c) 10%
(d) 12%

Question: Two particles X and Y having equal charges, after being accelerated through the same potential difference, enter a region of uniform magnetic field and describe circular paths of radii R1 and R2, respectively. The ratio of masses of X
(a) (R1/R2)1/2
(b) (R2/R1)
(c) (R1/R2)2
(d) (R1/R2)

Question: Choose the correct option

Assertion : Free electrons 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.
Reason : The average velocity of free electron is zero.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Question: A deuteron of kinetic energy 50 keV is describing a circular orbit of radius 0.5 metre in a plane perpendicular to the magnetic field B. The kinetic energy of the proton that describes a circular orbit of radius 0.5 metre in the same plane with the same B is
(a) 25 keV
(b) 50 keV
(c) 200 keV
(d) 100 keV

Question: According to oersted, around a current carrying conductor, magnetic field exists
(a) as long as there is current in the wire
(b) even after removing the current in the wire
(c) only few seconds after removing the current
(d) None of these

Question: Similarities of Biot–Savart’s law and Coulomb’s law for the electrostatics are
I. both are long range and inversely proportional to the square of distance from the source to the point of interest.
II. both are linear in source.
III. both are produced by scalar sources.
IV. both follow principle of superposition.
(a) I, II and III
(b) II, III and IV
(c) I, II and IV
(d) I, III and IV

Question: Ampere’s circuital law states that
(a) the surface integral of magnetic field over the open surface is equal to μ0 times the total current passing through the surface.
(b) the surface integral of magnetic field over the open surface is equal to μ0 times the total current passing near the surface.
(c) the line integral of magnetic field along the boundary of the open surface is equal to μ0 times the total current passing near the surface.
(d) the line integral of magnetic field along the boundary of the open surface is equal to μ0 times the total current passing through the surface.

Question: Biot-Savart law indicates that the moving electrons velocity
(V) produce a magnetic field B such that
(a) B ∥ V
(b) B ⊥ V
(c) it obeys inverse cube law
(d) it is along the line joining electron and point of observation

Question: Ampere’s circuital law is equivalent to
(a) Biot-Savart law
(b) Coulomb’s law
(d) Kirchhoff’s law

Question: The current sensitivity of a galvanometer is defined as
(a) the current flowing through the galvanometer when a unit voltage is applied across its terminals.
(b) current per unit deflection.
(c) deflection per unit current.
(d) dflection per unit current when a unit voltage is applied across its terminals

Question: The magnetic field around a long straight current carrying wire is
(a) spherical symmetry
(b) cylindrical symmetry
(c) cubical symmetry
(d) unsymmetrical

Question: If a copper rod carries a direct current, the magnetic field associated with the current will be
(a) only inside the rod
(b) only outside the rod
(c) both inside and outside the rod
(d) neither inside nor outside the rod

Question: Magnetic field at the centre of a circular coil of radius r, through which a current I flows is
(a) directly proportional to r
(b) inverseley proportional to I
(c) directly proportional to I
(d) directly proprotional to I2

Question: Two parallel circular coils of equal radii having equal number of turns placed coaxially and separated by a distance equal to the radii of the coils carrying equal currents in same direction are known as
(a) Biot-savart’s coils
(b) Ampere’s coils
(c) Helmholtz coils
(d) Oersted’s coils.

Question: Magnetic field inside a solenoid is
(a) directly proportional to its length
(b) directly proportional to current
(c) inversely proportional to total number of turns
(d) inversely porportional to current

Question: A long solenoid has a radius a and number of turns per unit length n. If it carries a current i, then the magnetic field on its axis is directly proportional to
(a) ani
(b) ni
(c) ni /a
(d) n2i

Question: If a current is passed through a spring then the spring will
(a) expand
(b) compress
(c) remains same
(d) None of these

Question: Lorentz force is
(a) electrostatic force acting on a charged particle.
(b) magnetic force acting on a moving charged particle.
(c) the vector sum of electrostatic and magnetic force acting on a moving charged particle.
(d) the vector sum of gravitational and magnetic force acting on a moving charged particle.

Question: A moving coil galvanometer has N number of turns in a coil of effective area A, it carries a current I. The magnetic field B is radial. The torque acting on the coil is
(a) NA2B2I
(b) NABI2
(c) N2ABI
(d) NABI

Question: Which of the following is true ?
(a) Parallel currents repel, and antiparallel currents attract.
(b) Parallel currents attract, and antiparallel currents repel.
(c) Both parallel and antiparallel currents attract.
(d) Both parallel and antiparallel currents repel.

Question: Which of the following is the correct definition of ampere?
(a) The ampere is the value of that steady current which when maintained in each of the two very long, straight, parallel conductors of negligible cross-section, and placed one metre apart in vacuum, would produce on each of these conductors a force equal to 2 × 107 N/m of length.
(b) The ampere is the value of that steady current which when maintained in each of the two very long, straight, parallel conductors of negligible cross-section, and placed one centimetre apart in vacuum, would produce on each of these conductors a force equal to 2 × 10–7 N/m of length.
(c) The ampere is the value of that steady current which, when maintained in each of the two very long, straight, parallel conductors of negligible cross-section, and placed one metre apart in vacuum, would produce on each of these conductors a force equal to 2 × 10–7 N/m of length.
(d) The ampere is the value of that steady current which, when maintained in each of the two very long, straight, parallel conductors of negligible cross-section, and placed ten metre apart in vacuum, would produce on each of these conductors a force equal to 2 × 10–7 N/m of length.

Question: An electron having a charge e moves with a velocity v in X-direction. An electric field acts on it in Y-direction? The force on the electron acts in
(a) positive direction of Y-axis
(b) negative direction of Y-axis
(c) positive direction of Z-axis
(d) negative direction of Z-axis

Question: An electric charge in uniform motion produces
(a) an electric field only
(b) a magnetic field only
(c) both electric and magnetic fields
(d) no such field at all

Question: If a long hollow copper pipe carries a direct current, the magnetic field associated with the current will be
(a) only inside the pipe
(b) only outside the pipe
(c) neither inside nor outside the pipe
(d) both inside and outside the pipe

Question: Energy in a current carrying coil is stored in the form of
(a) electric field
(b) magnetic field
(c) dielectric strength
(d) heat

Question: Two free parallel wires carrying currents in the opposite directions
(a) attract each other
(b) repel each other
(c) do not attract each other
(d) get rotated to be perpendicular to each other

Question: Two parallel wires carrying currents in the same direction attract each other because of
(a) potential difference between them
(b) mutual inductance between them
(c) electric forces between them
(d) magnetic forces between them

Question: A wire is placed parallel to the lines of force in a magnetic field and a current flows in the wire. Then
(a) the wire will experience a force in the direction of the magnetic field
(b) the wire will not experience any force at all
(c) the wire will experience a force in a direction opposite to the field
(d) it experiences a force in a direction perpendicular to lines of force

Question: A current carrying loop is placed in a uniform magnetic field. The torque acting on it does not depend upon
(a) shape of the loop
(b) area ot the loop
(c) value of the current
(d) magnetic field

Question: A charged particle moves through a magnetic field in a direction perpendicular to it. Then the
(a) velocity remains unchanged
(b) speed of the particle remains unchanged
(c) direction of the particle remains unchanged
(d) acceleration remains unchanged

Question: Consider a moving charged particle in a region of magnetic field. Which of the following statements are correct ?
I. If v is parallel to B, then path of particle is spiral.
II. If v is perpendicular to B, then path of particle is a circle.
III. If v has a component along B, then path of particle is helical.
IV. If v is along B, then path of particle is a circle.
(a) I and II
(b) II and III
(c) III and IV
(d) IV and I

Question: Direction of force due to magnetic field on a moving charged particle is
I. perpendicular to direction of velocity of charged particle.
II. perpendicular to direction of magnetic field.
III. parallel to direction of velocity of charged particle.
IV. parallel to the direction of magnetic field.
Correct statements are
(a) I and IV
(b) I and II
(c) I and III
(d) III and IV

Question:
In cyclotron the gyro radius is
(a) proportional to momentum
(b) proportional to energy
(c) inversely proportional to momentum
(d) inversely proportional to energy

Question:
In cyclotron the resonance condition is
(a) the frequency of revolution of charged particle is equal to the frequency of A.C. voltage sources
(b) the frequency of revolution of charged particle is equal to the frequency of applied magnetic field
(c) the frequency of revolution of charged particle is equal to the frequency of rotation of earth
(d) the frequency of revolution of charged particle, frequency of A.C. source and frequency of magnetic field are equal

Question:
A charge q is moving with a velocity v parallel to a magnetic field B. Force on the charge due to magnetic field is
(a) q v B
(b) q B/v
(c) zero
(d) B v/q

Question:
A particle of mass m and charge q enters a magnetic field B perpendicularly with a velocity v. The radius of the circular path described by it will be
(a) Bq / mv
(b) mq / Bv
(c) mB / qv
(d) mv / Bq

Question:
Cyclotron is used to accelerate
(a) electrons
(b) neutrons
(c) positive ions
(d) negative ions

Question:
The magnetic dipole moment of a current loop is independent of
(a) magnetic field in which it is lying
(b) number of turns
(c) area of the loop
(d) current in the loop

Question:
Magnetic dipole moment of a rectangular loop is
(a) inversely proportional to current in loop
(b) inversely proportional to area of loop
(c) parallel to plane of loop and porportional to area of loop
(d) perpendicular to plane of loop and porportional to area of loop

Question:
Consider the following statements and select the incorrect statement(s).
I. The presence of a large magnetic flux through a coil maintains a current in the coil if the circuit is continuous
II. A coil of a metal wire kept stationary in a non– uniform magnetic field has an e.m.f induced in it
III. A charged particle enters a region of uniform magnetic field at an angle of 85° to the magnetic lines of force, the path of the particle is a circle
IV. There is no change in the energy of a charged particle moving in a magnetic field although a magnetic force is acting on it
(a) I and II
(b) II and III
(c) II only
(d) IV only

Question:
The magnetic moment of a circular coil carrying current is
(a) directly proportional to the length of the wire in the coil
(b) inversely proportional to the length of the wire in the coil
(c) directly proportional to the square of the length of the wire in the coil
(d) inversely proportional to the square of the length of the wire in the coil

Question:
To make the field radial in a moving coil galvanometer
(a) the number of turns in the coil is increased
(b) magnet is taken in the form of horse-shoe
(c) poles are cylindrically cut
(d) coil is wounded on aluminium frame

Question:
The deflection in a moving coil galvanometer is
(a) directly proportional to the torsional constant
(b) directly proportional to the number of turns in the coil
(c) inversely proportional to the area of the coil
(d) inversely proportional to the current flowing

Question: In a moving coil galvanometer, the deflection of the coil
θ is related to the elecrical current i by the relation
(a) i ∝ tan θ
(b) i ∝θ
(c) i ∝ θ2
(d) i ∝ θ

Question: A coil of circular cross-section having 1000 turns and 4 cm2 face area is placed with its axis parallel to a magnetic field which decreases by 10–2 Wb m–2 in 0.01 s. The e.m.f. induced in the coil is:

(a) 400 mV

(b) 200 mV

(c) 4 mV

(d) 0.4 mV

Question: A charged particle moves through a magnetic field perpendicular to its direction. Then

(a) kinetic energy changes but the momentum is constant

(b) the momentum changes but the kinetic energy is constant

(c) both momentum and kinetic energy of the particle are not constant

(d) both momentum and kinetic energy of the particle are constant

Question: A metallic rod of mass per unit length 0.5 kg m–1 is lying horizontally on a smooth inclined plane which makes an angle of 30°with the horizontal. The rod is not allowed to slide down by flowing a current through it when a magnetic field of induction 0.25 T is acting on it in the vertical direction. The current flowing in the rod to keep it stationary is

(a) 7.14 A

(b) 5.98 A

(c) 11.32 A

(d) 14.76 A

Question: Choose the correct option

Assertion: The frequency of circular motion of a charged particle in cyclotron is independent of the mass of the particle.
Reason: Greater the mass of the particle less will be the frequency of the particle

(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Question:  A charged particle enters in a uniform magnetic field with a certain velocity. The power delivered to the particle by the magnetic field depends on

(a) force exerted by magnetic field and velocity of the particle.

(b) angular speed w and radius r of the circular path.

(c) angular speed w and acceleration of the particle.

(d) None of these

Question:  The length of a solenoid is 0.4 m and the number turns in it is 500. A current of 3 amp, is flowing in it. In a small coil of radius 0.01 m and number of turns 10, a current of 0.4 amp. is flowing. The torque necessary to keep the axis of this coil perpendicular to the axis of solenoid will be

(a) 5.92 × 10–6 N-m

(b) 5.92 × 10–4 N-m

(c) 5.92 × 10–6 dyne-cm

(d) 5.92 × 10–4 dyne-cm

Question: The AC voltage across a resistance can be measured using a

(a) hot wire voltmeter
(b) moving coil galvanometer
(c) potential coil galvanometer
(d) moving magnet galvanometer

Question: The deflection in a moving coil galvanometer is

(a) directly proportional to the torsional constant
(b) directly proportional to the number of turns in the coil
(c) inversely proportional to the area of the coil
(d) inversely proportional to the current flowing

Question:  The current sensitivity of a galvanometer is defined as

(a) the current flowing through the galvanometer when a unit voltage is applied across its terminals.
(b) current per unit deflection.
(c) deflection per unit current.
(d) dflection per unit current when a unit voltage is applied across its terminals

Question: A milli voltmeter of 25 milli volt range is to be converted into an ammeter of 25 ampere range. The value (in ohm) of necessary shunt will be

(a) 0.001

(b) 0.01

(c) 1

(d) 0.05

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