# MCQ Questions Chapter 4 Moving Charges and Magnetism Class 12 Physics

Please refer to MCQ Questions Chapter 4 Moving Charges and Magnetism Class 12 Physics with answers provided below. These multiple-choice questions have been developed based on the latest NCERT book for class 12 Physics issued for the current academic year. We have provided MCQ Questions for Class 12 Physics for all chapters on our website. Students should learn the objective based questions for Chapter 3 Moving Charges and Magnetism in Class 12 Physics provided below to get more marks in exams.

## Chapter 4 Moving Charges and Magnetism MCQ Questions

Please refer to the following Chapter 3 Moving Charges and Magnetism MCQ Questions Class 12 Physics with solutions for all important topics in the chapter.

MCQ Questions Answers for Chapter 4 Moving Charges and Magnetism Class 12 Physics

Question. When a proton is released from rest in a room, it starts with an initial acceleration a0 towards west. When it is projected towards north with a speed v0 it moves with an initial acceleration 3a0 toward west. The electric and magnetic fields in the room are

D

Question. A long straight wire carries a certain current and produces a magnetic field 2 × 10–4 Wb m–2 at a perpendicular distance of 5 cm from the wire. An electron situated at 5 cm from the wire moves with a velocity 107 m/s towards the wire along perpendicular to it. The force experienced by the electron will be (charge on electron 1.6 × 10–19 C)
(a) 3.2 N
(b) 3.2 × 10–16 N
(c) 1.6 × 10–16 N
(d) zero

B

Question. A uniform electric field and a uniform magnetic field are acting along the same direction in a certain region. If an electron is projected in the region such that its velocity is pointed along the direction of fields, then the electron
(a) will turn towards right of direction of motion
(b) speed will decrease
(c) speed will increase
(d) will turn towards left of direction of motion.

B

Question. A very long straight wire carries a current I. At the instant when a charge +Q at point P has velocity v¯, as shown, the force on the charge is

(a) along Oy
(b) opposite to Oy
(c) along Ox
(d) opposite to Ox.

A

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) 14.76 A
(d) 11.32 A

D

Question. A charge q moves in a region where electric field and magnetic field both exist, then force on it is

B

Question. A straight wire of length 0.5 metre and carrying a current of 1.2 ampere is placed in uniform magnetic field of induction 2 tesla. The magnetic field is perpendicular to the length of the wire. The force on the wire is
(a) 2.4 N
(b) 1.2 N
(c) 3.0 N
(d) 2.0 N.

B

Question. Tesla is the unit of
(a) electric field
(b) magnetic field
(c) electric flux
(d) magnetic flux

B

Question. A proton and an alpha particle both enter a region of uniform magnetic field B, moving at right angles to the 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) 1.5 MeV
(b) 1 MeV
(c) 4 MeV
(d) 0.5 MeV

B

Question. A proton carrying 1 MeV kinetic energy is moving in a circular path of radius R in uniform magnetic field. What should be the energy of an a-particle to describe a circle of same radius in the same field?
(a) 2 MeV
(b) 1 MeV
(c) 0.5 MeV
(d) 4 MeV

B

Question. A charge moving with velocity v in X-direction is subjected to a field of magnetic induction in negative X-direction. As a result, the charge will
(a) remain unaffected
(b) start moving in a circular path Y-Z plane
(c) retard along X-axis
(d) moving along a helical path around X-axis.

A

Question. The magnetic force acting on a charged particle of charge –2 μC in a magnetic field of 2 T acting in y direction, when the particle velocity is
(2^i+ 3^j)×106 ms−1 is
(a) 4 N in z direction
(b) 8 N in y direction
(c) 8 N in z direction
(d) 8 N in –z direction.

D

Question. When a charged particle moving with velocity v¯ is subjected to a magnetic field of induction B¯, the force on it is non-zero. This implies that
(a) angle between is either zero or 180°
(b) angle between is necessarily 90°
(c) angle between can have any value other than 90°
(d) angle between can have any value other than zero and 180°.

D

Question. Ionized hydrogen atoms and a-particles with same momenta enters perpendicular to a constant magnetic field, B. The ratio of their radii of their paths rH : ra will be
(a) 1 : 4
(b) 2 : 1
(c) 1 : 2
(d) 4 : 1

B

Question. Under the influence of a uniform magnetic field, a charged particle moves with a constant speed v in a circle of radius R. The time period of rotation of the particle
(a) depends on R and not on v
(b) is independent of both v and R
(c) depends on both v and R
(d) depends on v and not on R.

B

Question. A particle of mass m, charge Q and kinetic energy T enters in a transverse uniform magnetic field of induction B. After 3 seconds the kinetic energy of the particle will be
(a) T
(b) 4T
(c) 3T
(d) 2T

A

Question. A uniform magnetic field acts right angles to the direction of motion of electrons. As a result, the electron moves in a circular path of radius 2 cm. If the speed of electrons is doubled, then the radius of the circular path will be
(a) 2.0 cm
(b) 0.5 cm
(c) 4.0 cm
(d) 1.0 cm

C

Question. A deuteron of kinetic energy 50 keV is describing a circular orbit of radius 0.5 metre in a plane perpendicular to 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

D

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

A

Question. A beam of electrons is moving with constant velocity in a region having electric and magnetic fields of strength 20 V m–1 and 0.5 T at right angles to the direction of motion of the electrons. What is the velocity of the electrons?
(a) 8 m s–1
(b) 5.5 m s–1
(c) 20 m s–1
(d) 40 m s–1

D

Question. An electron having mass m and kinetic energy E enter in uniform magnetic field B perpendicularly, then its frequency will be

C

Question. A 10 eV electron is circulating in a plane at right angles to a uniform field at magnetic induction 10–4 Wb/m2 (= 1.0 gauss), the orbital radius of electron is
(a) 11 cm
(b) 18 cm
(c) 12 cm
(d) 16 cm

A

Question. An alternating electric field, of frequency u, is applied across the dees (radius = R) of a cyclotron that is being used to accelerate protons (mass = m). The operating magnetic field (B) used in the cyclotron and the kinetic energy (K) of the proton beam, produced by it, are given by

C

Question. The magnetic field dB¯ due to a small current element dl¯ at a distance r¯ and element carrying current i is

B

Question. A particle having a mass of 10–2 kg carries a charge of 5 × 10–8 C. The particle is given an initial horizontal velocity of 105 m s–1 in the presence of electric field E and magnetic field B. To keep the particle moving in a horizontal direction, it is necessary that
(1) B should be perpendicular to the direction of velocity and E should be along the direction of velocity
(2) Both B and E should be along the direction of velocity
(3) Both B and E are mutually perpendicular and perpendicular to the direction of velocity.
(4) B should be along the direction of velocity and E should be perpendicular to the direction of velocity Which one of the following pairs of statements is possible?
(a) (1) and (3)
(b) (3) and (4)
(c) (2) and (3)
(d) (2) and (4)

C

Question. A beam of electron passes undeflected through mutually perpendicular electric and magnetic fields. If the electric field is switched off, and the same magnetic field is maintained, the electrons move
(a) in a circular orbit
(b) along a parabolic path
(c) along a straight line
(d) in an elliptical orbit.

A

Question. A charge having e/m equal to 108 C/kg and with velocity 3 × 105 m/s enters into a uniform magnetic field B = 0.3 tesla at an angle 30° with direction of field. The radius of curvature will be
(a) 0.01 cm
(b) 0.5 cm
(c) 1 cm
(d) 2 cm

D

Question. A positively charged particle moving due East enters a region of uniform magnetic field directed vertically upwards. This particle will
(a) move in a circular path with a decreased speed
(b) move in a circular path with a uniform speed
(c) get deflected in vertically upward direction
(d) move in circular path with an increased speed.

B

Question. In a mass spectrometer used for measuring the masses of ions, the ions are initially accelerated by an electric potential V and then made to describe semicircular paths of radius R using a magnetic field B. If V and B are kept constant, the ratio (charge on the ion/mass of the ion) will be proportional to
(a) 1/R2
(b) R2
(c) R
(d) 1/R

A

Question. To convert a galvanometer into a voltmeter one should connect a
(a) high resistance in series with galvanometer
(b) low resistance in series with galvanometer
(c) high resistance in parallel with galvanometer
(d) low resistance in parallel with galvanometer.

A

Question. A galvanometer having a resistance of 9 ohm is shunted by a wire of resistance 2 ohm. If the total current is 1 amp, the part of it passing through the shunt will be
(a) 0.2 amp
(b) 0.8 amp
(c) 0.25 amp
(d) 0.5 amp

B

Question. In Thomson mass spectrograph E¯ ⊥ B¯ then the velocity of electron beam will be

A

Question. A straight conductor carrying current i splits into two parts as shown in the figure. The radius of the circular loop is R. The total magnetic field at the centre P at the loop is

(a) Zero
(b) 3μ0i/32R, outward
(c) 3μ0i/32R, inward
(d) (μ0i/2R), inward

A

Question. Two circular coils 1 and 2 are made from the same wire but the radius of the 1st coil is twice that of the 2nd coil. What potential difference in volts should be applied across them so that the magnetic field at their centres is the same?
(a) 2
(b) 3
(c) 4
(d) 6

B

Question. An electron moves in a circular orbit with a uniform speed v. It produces a magnetic field B at the centre of the circle. The radius of the circle is proportional to

C

Question. Two similar coils of radius R are lying concentrically with their planes at right angles to each other. The currents flowing in them are I and 2I, respectively. The resultant magnetic field induction at the centre will be

A

Question. Charge q is uniformly spread on a thin ring of radius R. The ring rotates about its axis with a uniform frequency f Hz. The magnitude of magnetic induction at the center of the ring is
(a) μ0qf/2πR
(b) μ0qf/2R
(c) μ0q/2fR
(d) μ0q/2πfR

B

Question. A long wire carrying a steady current is bent into a circular loop of one turn. The magnetic field at the centre of the loop is B. It is then bent into a circular coil of n turns. The magnetic field at the centre of this coil of n turns will be
(a) nB
(b) n2B
(c) 2nB
(d) 2n2B.

B

Question. A wire carrying current I has the shape as shown in adjoining figure. Linear parts of the wire are very long and parallel to X-axis while semicircular portion of radius R is lying in Y-Z plane. Magnetic field at point O is

A

Question. A current loop consists of two identical semicircular parts each of radius R, one lying in the x-y plane and the other in x-z plane. If the current in the loop is i. The resultant magnetic field due to the two semicircular parts at their common centre is

A

Question. The magnetic field of given length of wire for single turn coil at its centre is B then its value for two turns coil for the same wire is
(a) B/4
(b) B/2
(c) 4B
(d) 2B

C

Question. Magnetic field due to 0.1 A current flowing through a circular coil of radius 0.1 m and 1000 turns at the centre of the coil is
(a) 6.28 × 10–4 T
(b) 4.31 × 10–2 T
(c) 2 × 10–1 T
(d) 9.81 × 10–4 T

A

Question. The magnetic field at centre, P will be

C

Question. A straight wire of diameter 0.5 mm carrying a current of 1 A is replaced by the another wire of 1 mm diameter carrying the same current. The strength of the magnetic field far away is
(a) one-quarter of the earlier value
(b) one-half of the earlier value
(c) twice the earlier value
(d) same as the earlier value.

D

Question. Magnetic field intensity at the centre of the coil of 50 turns, radius 0.5 m and carrying a current of 2 A, is
(a) 3 × 10–5 T
(b) 1.25 × 10–4 T
(c) 0.5 × 10–5 T
(d) 4 × 106

B

Question. A long straight wire of radius a carries a steady current I. The current is uniformly distributed over its cross-section. The ratio of the magnetic fields B and B′, at radial distances a/2 and 2a respectively, from the axis of the wire is
(a) 1
(b) 4
(c) 1/4
(d) 1/2

A

Question. Two identical long conducting wires AOB and COD are placed at right angle to each other, with one above other such that O is their common point for the two. The wires carry I1 and I2 currents, respectively. Point P is lyng at distance d from O along a direction perpendicular to the plane containing the wires. The magnetic field at the point P will be

D

Question. If a long hollow copper pipe carries a current, then produced magnetic field will be
(a) both inside and outside the pipe
(b) outside the pipe only
(c) inside the pipe only
(d) neither inside nor outside the pipe.

B

Question. A galvanometer has a coil of resistance 100 ohm and gives a full scale deflection for 30 mA current. If it is work as a voltmeter of 30 volt range, the resistance required to be added will be
(a) 900 Ω
(b) 1800 Ω
(c) 500 Ω
(d) 1000 Ω.

A

Question. A coil of one turn is made of a wire of certain length and then from the same length a coil of two turns is made. If the same current is passed in both the cases, then the ratio of the magnetic inductions at their centres will be
(a) 4 : 1
(b) 1 : 4
(c) 2 : 1
(d) 1 : 2

B

Question. A cylindrical conductor of radius R is carrying a constant current. The plot of the magnitude of the magnetic field, B with the distance, d from the centre of the conductor, is correctly represented by the figure

D

Question. A galvanometer having a coil of resistance 60 Ω shows full scale deflection when a current of 1.0 amp passes through it. It can be converted into an ammeter to read currents upto 5.0 amp by
(a) putting in series a resistance of 15 Ω
(b) putting in series a resistance of 240 Ω
(c) putting in parallel a resistance of 15 Ω
(d) putting in parallel a resistance of 240 Ω.

C

Question. Two equal electric currents are flowing perpendicular to each other as shown in the figure. AB and CD are perpendicular to each other and symmetrically placed with respect to the currents. Where do we expect the resultant magnetic field to be zero?

(a) On CD
(b) On AB
(c) On both OD and BO
(d) On both AB and CD

B

Question. The magnetic field at a distance r from a long wire carrying current i is 0.4 tesla. The magnetic field at a distance 2r is
(a) 0.2 tesla
(b) 0.8 tesla
(c) 0.1 tesla
(d) 1.6 tesla

A

Question. A rectangular coil of length 0.12 m and width 0.1 m having 50 turns of wire is suspended vertically in a uniform magnetic field of strength 0.2 Weber/m2. The coil carries a current of 2 A. If the plane of the coil is inclined at an angle of 30° with the direction of the field, the torque
required to keep the coil in stable equilibrium will be
(a) 0.24 N m
(b) 0.12 N m
(c) 0.15 N m
(d) 0.20 N m

D

Question. A current loop in a magnetic field
(a) can be in equilibrium in two orientations, both the equilibrium states are unstable.
(b) can be in equilibrium in two orientations, one stable while the other is unstable.
(c) experiences a torque whether the field is uniform or non uniform in all orientations.
(d) can be in equilibrium in one orientation.

B

Question. A circular loop of area 0.01 m2 carrying a current of 10 A, is held perpendicular to a magnetic field of intensity 0.1 T. The torque acting on the loop is
(a) 0.001 N m
(b) 0.8 N m
(c) zero
(d) 0.01 N m.

C

Question. A coil carrying electric current is placed in uniform magnetic field
(a) torque is formed
(b) e.m.f is induced
(c) both (a) and (b) are correct
(d) none of these

A

Question. A current carrying coil is subjected to a uniform magnetic field. The coil will orient so that its plane becomes
(a) inclined at 45° to the magnetic field
(b) inclined at any arbitrary angle to the magnetic field
(c) parallel to the magnetic field
(d) perpendicular to magnetic field.

D

Question. Current sensitivity of a moving coil galvanometer is 5 div/mA and its voltage sensitivity (angular deflection per unit voltage applied) is 20 div/V. The resistance of the galvanometer is
(a) 40 W
(b) 25 W
(c) 250 W
(d) 500 W

C

Question. A galvanometer of resistance 50 W is connected to a battery of 3 V along with a resistance of 2950 Ω in series. A full scale deflection of 30 divisions is obtained in the galvanometer. In order to reduce this deflection to 20 divisions, the resistance in series should be
(a) 6050 Ω
(b) 4450 Ω
(c) 5050 Ω
(d) 5550 Ω

B

Question. The magnetic induction at a point P which is at the distance of 4 cm from a long current carrying wire is 10–3 T. The field of induction at a distance 12 cm from the current will be
(a) 3.33 × 10–4 T
(b) 1.11 × 10–4 T
(c) 33 × 10–3 T
(d) 9 × 10–3 T

A

Question. Two long parallel wires are at a distance of 1 metre. Both of them carry one ampere of current. The force of attraction per unit length between the two wires is
(a) 5 × 10–8 N/m
(b) 2 × 10–8 N/m
(c) 2 × 10–7 N/m
(d) 10–7 N/m

C

Question. The resistance of an ammeter is 13 Ω and its scale is graduated for a current upto 100 amps. After an additional shunt has been connected to this ammeter it becomes possible to measure currents upto 750 amperes by this meter. The value of shunt resistance is
(a) 2 Ω
(b) 0.2 Ω
(c) 2 kΩ
(d) 20 Ω

A

Question. A galvanometer of 50 ohm resistance has 25 divisions. A current of 4 × 10–4 ampere gives a deflection of one division. To convert this galvanometer into a voltmeter having a range of 25 volts, it should be connected with a resistance of
(a) 2500 Ω as a shunt
(b) 2450 Ω as a shunt
(c) 2550 Ω in series
(d) 2450 Ω in series.

D

Question. To convert a galvanometer into a ammeter, one needs to connect a
(a) low resistance in parallel
(b) high resistance in parallel
(c) low resistance in series
(d) high resistance in series.

A

Question. A closed loop PQRS carrying a current is placed in a uniform magnetic field. If the magnetic forces on segments PS, SR and RQ are F1, F2 and F3 respectively and are in the plane of the paper and along the directions shown, the force on the segment QP is

D

Question. A square current carrying loop is suspended in a uniform magnetic field acting in the plane of the loop. If the force on one arm of the loop is F¯ the net force on the remaining three arms of the loop is
(a) 3F¯
(b) −F¯
(c) −3F¯
(d) F¯

B

Question. A circular coil ABCD carrying a current ‘i’ is placed in a uniform magnetic field. If the magnetic force on the segment AB is F¯, the force on the remaining segment BCDA is
(a) −F¯
(b) 3F¯
(c) −3F¯
(d) F¯

A

Question. A square loop, carrying a steady current I, is placed in a horizontal plane near a long straight conductor carrying a steady current I1 at a distance d from the conductor as shown in figure. The loop will experience

(a) a net attractive force towards the conductor
(b) a net repulsive force away from the conductor
(c) a net torque acting upward perpendicular to the horizontal plane
(d) a net torque acting downward normal to the horizontal plane.

A

Assertion-Reason Questions

In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R). Choose the correct answer out of the following choices.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.

Question. Assertion (A): Magnetic lines of force form continuous closed loops whereas electric lines of force do not.
Reason (R): Magnetic poles always occur in pairs as north pole and south pole.

A

Question. Assertion (A): Motion of electron around a positively charged nucleus is different from the motion of a planet around the sun.
Reason (R): The force acting in both the cases is same in nature.

D

Question. Assertion (A): Galvanometer cannot as such be used as an ammeter to measure the value of the current in a given circuit.
Reason (R): It gives a full-scale deflection for a current of the order of micro ampere.

A

Question. Assertion (A): Two parallel conducting wires carrying currents in same direction, come close to each other.
Reason (R): Parallel currents attract and anti parallel currents repel.

A

Question. Assertion (A): Magnetic field is caused by current element.
Reason (R): Magnetic field due to a current element

B

Question. Assertion (A): Magnetic field lines always form closed loops.
Reason (R): Moving charges or currents produce a magnetic field.

B

Question. Assertion (A): A cyclotron does not accelerate electrons.
Reason (R): Mass of electron is very small, so it gains relativistic speed very soon.

A

Question. Assertion (A): A galvanometer can be used as an ammeter to measure the current across a given section of the circuit.
Reason (R): For this it must be connected in series with the circuit.

A

Question. Assertion (A): When a magnetic dipole is placed in a non uniform magnetic field, only a torque acts on the dipole.
Reason (R): Force would not act on dipole if magnetic field were non uniform.