CBSE Class 12 Physics Moving Charges And Magnetism Boards Questions Worksheet

 Important Questions for NCERT Class 12 Physics Moving Charges And Magnetism

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

(a) eE /qvB
(b) 2πm /eB
(c) eB /2πm
(d) 2m /eBE

Answer :  C

Question. Two parallel wires in free space are 10 cm apart and each carries a current of 10 A in the same direction. The force exerted by one wire on the other, per metre length is
(a) 2 × 10–4 N, repulsive
(b) 2 × 10–7N, repulsive
(c) 2 × 10–4 N, attractive
(d) 2 × 10–7N, attractive.

Answer :  C

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

Answer :  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.

Answer :  B

Question. A charged particle (charge q) is moving in a circle of radius R with uniform speed v. The associated magnetic moment m is given by
(a) qvR2
(b) qvR2/2
(c) qvR
(d) qvR/2

Answer :  D

Question. If number of turns, area and current through a coil is given by n, A and i respectively then its magnetic moment will be
(a) niA
(b) n2iA
(c) niA2
(d) ni /√A

Answer :  A

Question. Electron moves at right angles to a magnetic field of 1.5 × 10^–2 tesla with speed of 6 × 10⁷ m/s.
If the specific charge of the electron is 1.7 × 10¹¹ C/kg. The radius of circular path will be
(a) 3.31 cm
(b) 4.31cm
(c) 1.31 cm
(d) 2.35 cm

Answer :  D

Question. An electron beam passes through a magnetic field of 2 × 10^–3 Wb/m² and an electric field of 1.0 × 10⁴ V/m both acting simultaneously. The path of electron remains undeviated. The speed of electron if the electric field is removed, and the radius of electron path will be respectively
(a) 10 × 10⁶ m/s, 2.43 cm 
(b) 2.5 × 10⁶ m/s, 0.43 cm
(c) 5 × 10⁶ m/s, 1.43 cm
(d) none of these

Answer :  C

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

Answer :  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.

Answer :  A

Question. A charged particle is released from rest in a region of uniform electric and magnetic fields which areparallel to each other. The particle will move on a:
(a) straight line
(b) circle 
(c) helix
(d) cycloid

Answer :  A

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

Answer :  C

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. 

Answer :  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 

Answer :  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.

Answer :  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

Answer :  C

Question. In an ammeter 0.2% of main current passes through the galvanometer. If resistance of galvanometer is G, the resistance of ammeter will be
(a) 1 /499 G
(b) 499 /500 G
(c) 1 /500 G
(d) 500 /499 G 

Answer :  C

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

Answer :  A

Question. A galvanometer having a coil of resistance 60 W 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

Answer :  C

Question. A galvanometer of resistance 50 W is connected to a battery of 3 V along with a resistance of 2950 W 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

Answer :  B

Question. The resistance of an ammeter is 13 W 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 k Ω
(d) 20 Ω

Answer :  A

Question. A proton and an a-particle, moving with the same velocity, enter a uniform magnetic field, acting normal to the plane of their motion. The ratio of the radii of the circular paths described by the proton and a-particle is : 
(a) 1 : 2
(b) 1 : 4
(c) 4 : 1
(d) 1 : 16

Answer :  A

Question. A long straight wire of radius a carries a steady current i. The current is uniformly distributed across its cross section. The ratio of the magnetic field at a/2 and 2a is 
(a) 1/2
(b) 1/4
(c) 4
(d) 1

Answer :  D

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 W as a shunt
(b) 2450 W as a shunt
(c) 2550 W in series
(d) 2450 W in series. 

Answer :  D

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.

Answer :  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 

Answer :  B

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

Answer :  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 

Answer :  A

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.

Answer :  A

Question. What should be amount of current through the ring of radius of 5 cm so that field at the centre equal to the magnetic field of 7 × 10–5 Wb/m2, is
(a) 0.28 amp
(b) 5.57 amp 
(c) 2.8 amp
(d) none of these

Answer :  B

Question. A closely wound flat circular coil of 25 turns of wire has diameter of 10 cm which carries current of 4 amperes, the magnetic field at the centre of a coil will be :
(a) 1.256´10-3 tesla
(b) 1.679´10-5 tesla
(c) 1.512´10-5 tesla
(d) 2.28´10-4 tesla

Answer :  A

Question. Cyclotron is used to accelerate : 
(a) positive ion
(b) negative ion
(c) electron
(d) none of these

Answer :  A

Question. The magnetic field at a given point is 0.5 × 10–5 Wb m–2. This field is to be annulled by magnetic induction at the centre of a circular conducting loop of radius 5.0 cm . The current required to be flown in the loop is nearly
(a) 0.2 A
(b) 0.4 A
(c) 4A
(d) 40 A

Answer :  B

Question. An electron is travelling along the x-direction. It encounters a magnetic field in the y-direction.
Its subsequent motion will be : 
(a) straight line along the x-direction
(b) a circle in the xz-plane
(c) a circle in the yz-plane
(d) a circle in the xy-plane

Answer :  B

Question. The cyclotron frequency of an electrons gyrating in a magnetic field of 1 T is approximately :
(a) 28 MHz
(b) 280 MHz 
(c) 2.8 MHz
(d) 28 GHz

Answer :  D

Question. The magnetic moment of current (I) carrying circular coil of radius (r) and number of turns (n) varies as : 
(a) 1/r2
(b) 1/r
(c) r
(d) r2

Answer :  D

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)

Answer  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.

Answer  A

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

Answer  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

Answer  D

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.

Answer  B

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) √5μ0I /2R
(b)√5μ0I /R
(c) μ0I / 2R
(d) μ0I / R

Answer  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 / 2nR
(b) μ0qf / 2R
(c) μ0q / 2fR
(d) μ0q / 2nfR

Answer  B

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) μ₀i /2√2R
(b) μ₀i /2R
(c) μ₀i /4R
(d) μ₀i /√2R

Answer  A

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
(a) √B / v
(b) B/v
(c) √v / B
(d) v/B

Answer  C

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 

Answer  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 

Answer  A

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