# Physics Class 12th Chapter-4 Moving Charge And Magnetism Most VVI Objective Questions

Q.1. 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 the electron and point of observation.

Ans: (a)

Q.2. A Current loop placed in a non uniform magnetic field experinces

(a) a force of repulsion

(b) a force of attraction

(c) a torque but not force

(d) a force and a torque.

Ans :- (d)

Q.3. Unit of flux of magnetic field is

(A) Tesla

(B) Henry

(C) Weber

(D) joule second

Ans :- (C)

Q.4. S.I. unit of magnetic moment is

(A) JT⁻²

(B) Am²

(C) JT

(D) Am⁻¹

Ans :- (B)

Q.5. A voltmeter is always used in

(A) series in the circuit

(B) parallel in the circuit

(C) may be used in series and in parallel

(D) none of these

Ans :- (B)

Q.6. S.I. unit of pole strength is

(A) N

(B) N/A-m

(C) A-m

(D) T

Ans :- (C)

Q.7. Which of the following is likely to have the large resistance ?

(A) a galvanometer

(B) an ammeter

(C) a millivoltmeter

(D) a voltmeter

Ans :- (D)

Q.8. Which of the following is likely to have the least resistance ?

(A) a galvanometer

(B) an ammeter

(C) milliameter

(D) a voltmeter

Ans :- (B)

Q.9. An ideal voltmeter has

(A) zero resistance

(B) infinite resistance

(C) both ‘A’ and ‘B’

(D) none of these

Ans :- (B)

Q.10. If a current flows through a circular coil the magnetic field at the centre is

(A) in the plane of the coil

(B) at right angles to the plane of coil

(C) at an angle θ

(D) none of these

Ans :- (B)

Q.11. A charge moving with uniform velocity produces

(A) only an electric field

(B) only a magnetic field

(C) electromagnetic field

(D) none of these

Ans :- (B)

Q.12. If two parallel wires carry current in the same direction, the forces between them will be

(A) zero

(B) attractive

(C) repulsive

(D) infinite

Ans :- (B)

Q.13. Ampere’s circuital theorem (law) is analogous to

(A) Gravitational law

(B) Electrostatic coulomb’s law

(C) Gauss’s theorem

(D) none of these

Ans :- (C)

Q.14. Biot – savart law is analogous to

(A) coulomb’ law

(B) Newton’ law of motion

(C) Stoke’ s law

(D) Gauss’s law

Ans :- (A)

Q.15. The S.I. unit of the magnetic flux density is

(A) Tesla (π)

(B) Henry

(C) watt

(D) Weber

Ans :- (A)

Q.16. The S.I. unit of the magnetic field (B) is

(A) wb/m²

(B) Tesla

(C) Henry

(D) both ‘A’ and ‘B’

Ans :- (D)

Q.17. The shunt is used with a galvanometer to

(A) increases its sensitivity

(B) increases its resistance

(C) increases its range

(D) to protect it from damages

Ans :- (D)

Q.18. A device to converts mechanical energy to electrical energy is called

(A) a dynamo

(B) a.d.c. motor

(C) cyclotron

(D) none of these

Ans :- (A)

Q.19. The magnetic field induction at a point is a

(A) pseudo scalar quantity

(B) pseudo vector quantity

(C) axial vector

(D) none of these

Ans :- (B)

Q.20. When a charged particle moves perpendicular to magnetic field, then

(A) speed of the particle is changed

(B) speed of particle remains unchanged

(C) direction of the particle remains unchanged

(D) acceleration of the particle remains unchanged

Ans :- (B)

Q.21. A dynamo is sometimes said to generate electricity. If actually acts as a source of

(A) charge

(B) magnetism

(C) energy

(D) emf

Ans :- (D)

Q.22. Which of the following does not depend upon the magnetic effect

(A) moving coil galvanometer

(B) dynamo

(C) thermocouple

(D) d.c. motor

Ans :- (C)

Q.23. Magnetic dipole moment is a vector quantity directed from

(A) South to North pole

(B) north to south pole

(C) east to west direction

(D) west to east direction

Ans:- (A)

Q.24.  A charged particle is moving in a cyclotron, what effect on the radius of path of this charged particle will occur when the frequency of the ratio frequency field is doubled?

(a) It will also be doubled.

(b) It will be halved.

(c) It will be increased by four times.

(d) It will remain unchanged.

Q.25. Which of the following is not correct about cyclotron?

(a) It is a machine to accelerate charged particles or ions to high energies.

(b) Cyclotron uses both electric and magnetic fields in combination to increase the energy of charged particles.

(c) The operation of the cyclotron is based on the fact that the time for one revolution of an ion is independent of its speed or radius of its orbit.

(d) The charged particles and ions in cyclotron can move on any arbitrary path.

Q.26.  If an electron is moving with velocity ν⃗  produces a magnetic field B⃗ , then

(a) the direction of field B  will be same as the direction of velocity ν .

(b) the direction of field B⃗  will be opposite to the direction of velocity ν⃗  .

(c) the direction of field B⃗  will be perpendicular to the direction of velocity ν⃗  .

(d) the direction of field B⃗  does not depend upon the direction of velocity ν⃗  .

Q.27. The nature of parallel and anti-parallel currents are

(a) parallel currents repel and antiparallel cur¬rents attract.

(b) parallel currents attract and antiparallel cur-rents repel.

(c) both currents attract. ’

(d) both currents repel.

Q.28.  The magnetic moment of a current I carrying circular coil of radius r and number of turns N varies as

(a) 1r²

(b) 1r

(c) r

(d) r²

Q.29. A short bar magnet has a magnetic moment of 0. 65 J T-1, then the magnitude and direction of the magnetic field produced by the magnet at a distance 8 cm from the centre of magnet on the axis is

(a) 2.5 × 10-4 T, along NS direction

(b) 2.5 × 10-4 T along SN direction

(c) 4.5 × 10-4 T, along NS direction

(d) 4.5 × 10-4 T, along SN direction

Q.30. A current carrying loop is placed in a uniform magnetic field. The torqe acting on it does not depend upon

(a) area of loop

(b) value of current

(c) magnetic field

(d) None of these

Q.31. A moving coil galvanometer can be converted into an ammeter by

(a) introducing a shunt resistance of large value in series.

(b) introducing a shunt resistance of small value in parallel.

(c) introducing a resistance of small value in series.

(d) introducing a resistance of large value in parallel.

Q.32. The conversion of a moving coil galvanometer into a voltmeter is done by

(a) introducing a resistance of large value in series.

(b) introducing a resistance of small value in parallel.

(c) introducing a resistance of large value in parallel.

(d) introducing a resistance of small value in series.

Q.33. When a magnetic compass needle is carried nearby to a straight wire carrying current, then

(I) the straight wire cause a noticeable deflection in the compass needle.

(II) the alignment of the needle is tangential to an imaginary circle with straight wire as its centre and has a plane perpendicular to the wire

(a) (I) is correct

(b) (II) is correct

(c) both (I) and (II) are correct

(d) neither (I) nor (II) is correct

Q.34. A strong magnetic field is applied on a stationary electron. Then the electron

(a) moves in the direction of the field.

(b) remained stationary.

(c) moves perpendicular to the direction of the field.

(d) moves opposite to the direction of the field.

Q.35. In an inertial frame of reference, the magnetic force on a moving charged particle is F  Its value in another inertial frame of reference will be

(a) remained same

(b) changed due to change in the amount of charge

(c) changed due to change in velocity of charged particle

(d) changed due to change in field direction

Q.36.  Which one of the following is correct statement about magnetic forces?

(a) Magnetic forces always obey Newton’s third law.

(b) Magnetic forces do not obey Newton’s third law.

(c) For very high current, magnetic forces obey Newton’s third law.

(d) Inside low magnetic field, magnetic forces obey Newton’s third law.

Q.37.  A charged particle is moving on circular path with velocity v in a uniform magnetic field B, if the velocity of the charged particle is doubled and strength of magnetic field is halved, then radius becomes

(a) 8 times

(b) 4 times

(c) 2 times

(d) 16 times

Q.38. Two a-particles have the ratio of their velocities as 3 : 2 on entering the field. If they move in different circular paths, then the ratio of the radii of their paths is

(a) 2 : 3

(b) 3 : 2

(c) 9 : 4

(d) 4 : 9

Q.39. A  current carrying conductor produces
(a) an electric field only
(b) a magnetic field only
(c) both magnetic and electric fields
(d) none of these
Q.40. Magnetic field lines due to a straight current are
(a) linear and parallel to the current
(b) linear and perpendicular to the current
(c) circular around the current
(d) none of these
Q.41. The shunt is used with a galvanometer to
(a) increase its sensitivity
(b) increase its resistance
(c) increase its range
(d) to protect it from damges
Q.42. A device to converts electrical energy to mechanical energy is called
(a) a dynamo
(b) a.d.c. motor
(c) cyclotron
(d) none of these
Q.43. Which of the following does not depend upon the magnetic effect
(a) moving coil galvanometer
(b) dynamo
(c) thermocouple
(d) d.c. motor
Q.44. The magnetic field at the centre of a circular coil of a fixed number of turns varies
(a) Directly as the current and inversely proportional to its radius
(b) inversely as the current and directly as the radius
(c) directly as the current and the radius
(d) none of these
Q.45. A bar magnet of magnetic moment M is cut into two parts of equal length. The magnetic moment of either part is
(a) M
(b) M\2
(c) 2M
(d) Zero
Q.46. A charged particle moves through a magnetic field. the effect of the field is to change the particles
(a) speed
(b) direction of motion
(c) energy
(d) acceleration
Q.47. A Electron having charge e and mass m is moving a uniform electric field. It’s acceleration will be
(a) e²\m
(b)  e²E\m
(c) eE\m
(d) none of these
Q.48. A Dynamo is sometimes said to generate electricity. its actually acts as a source of
(a) Charge
(b) magnetism
(c) energy
(d) emf
Q.49. A shunt is low resistance connected to a galvanometer
(a) in series to it
(b) in parallel to it
(c) anywhere in the circuit
(d) none of these