# Moving Charge and Magnetic Field MCQ Type Questions for ISC Class-12 Physics Ch-7

Moving Charge and Magnetic Field MCQ Type Questions for ISC Class-12 Ch-7 Physics . These MCQ  / Objective Type Questions is based on latest reduced syllabus according 2021-22 session on bifurcated pattern. Visit official website CISCE for detail information about ISC Board Class-12 Physics.

 Board ISC Class 12th (XII) Subject Physics Chapter-7 Moving Charge and Magnetic Field Syllabus on bifurcated syllabus (after reduction) Session 2021-22 Topic MCQ / Objective Type Question

### Chapter-7 Moving Charge and Magnetic Field MCQ Type Questions for ISC Class-12 Physics

Question 1: In a cyclotron, a charged particle

(a) undergoes acceleration all the time.
(b) speeds up between the does because of the magnetic field.
(c) speeds up in a dee.
(d) slows down within a dee and speeds up between dee.

Answer: (a) undergoes acceleration all the time.

Question 2:  A charged particle will not move with a constant velocity in a region where in,

(a) E = 0, B ≠ 0
(b) E ≠ 0, B ≠ 0
(c) E ≠ 0, B = 0
d) E = 0, B = 0.

Answer: (c) E ≠ 0, B = 0

Question 3:  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.

Answer: (d) The electron will continue to move with uniform velocity along the axis of the solenoid.

Question 4: 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.

Question 5:  What happens to the magnetic field at the centre of a circular current carrying coil if we double the radius of the coil keeping the current unchanged?

(a) halved
(b) doubled
(d) remains unchanged

Question 6: 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.

Answer: (d) It will remain unchanged.

Question 7: The nature of parallel and anti-parallel currents are

(a) parallel currents repel and antiparallel currents attract.
(b) parallel currents attract and antiparallel cur-rents repel.
(c) both currents attract. ’
(d) both currents repel.

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

Question 8:  The magnetic moment of a 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

Question 9:  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

Answer: (b) 2.5 × 10-4 T along SN direction

Question 10: 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

Answer  (a) The magnitude of magnetic moment now diminishes

Question 11:  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

Answer (d) The electron will continue to move with uniform velocity along the axis of the solenoid

Question 12: 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 13:  A charge moving with a velocity v in X-direction is subjected to a field of magnetic induction in the negative X direction. As a result, the charge will:

(a) remain undefeated
(b) retard along X-axis
(c) start moving in a circular path in YZ plane.
(d) move along a helical path around X-axis.

Question 14:  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 experience a force in a direction opposite to the magnetic field.
(c) It will experience a force in a direction perpendicular to the lines of force.
(d) Tire wire will not experience a force at all.

Answer (d) Tire wire will not experience a force at all.

Question 15: In order to increase the sensitivity of a moving coil galvanometer,

(a) the suspension wire should be made stiff.
(b) the arc of the coil should be reduced.
(c) the magnetic field should be increased.
(d) the number of turns in the coil should be reduced.

Question 16: The current sensitibility of a moving coil galanometer increases with decrease in:

(a) magnetic field
(b) area of a coil
(c) number of turns
(d) None of these

Question 17:  A current carring coil is placed in a uniform magnetic field. If the coil turns through an angle θ, then the torque is directly proportional to:

(a) sin θ
(b) cos θ
(c) cot θ
(d) tan θ

Question 18:  Two solenoids having lengths L and 2L and the number of loops N and 4N, both have the same current, then the ratio of the magnetic field will be

(a) 1 : 2
(b) 2 : 1
(c) 1 : 4
(d) 4 : 1

Question 19:  A circular current loop of magnetic moment Mis in an arbitrary orientation in an external magnetic field B. The work done to rotate the loop by 30° about an axis perpendicular to its plane is

(a) MB
(b) √3MB2
(c) MB2
(d) zero

Question 20:  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.

Question 21: 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

Question 22: 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.

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

Question 23: 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

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

Question 24:  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.

Question 25: 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 26:  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 27:  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.

Answer  (b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion

Question 28:    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 29:    When a charged particle moves perpendicular to a uniform magnetic field, its:

(a) Energy and momentum both change.
(b) Energy and momentum both don’t change.
(c) Energy changes but momentum remains unchanged.
(d) Momentum changes but energy remains unchanged.

Answer (d) Momentum changes but energy remains unchanged.

Question 30:    The force on a current carrying conductor in a magnetic field is maximum, when angle between the length of the conductor and the magnetic field is:

(a) π/2
(b) π/4
(c) π
(d) zero

Question 31:  Two protons move parallel to each other with equal speeds 3 × 102 m/s. The ratio of magnetic and electrical forces between them is:

(a) 10-6
(b) 10-3
(c) 10-9
(d) 1

Question 32:   A proton and an a particle enter in a uhiform magnetic field with the same velocity. The period of rotation of the α-particle will be:

(a) four times that of the proton.
(b) three times that of the proton.
(c) two times that of the proton.
(d) same as that of the proton.

Answer (c) two times that of the proton.

Question 33:  A circular of radius R carries a current I. The magnetic field at its centre is B. At what distance from the centre on the axis of the coil, the magnetic field will be B/8?

(a) √2R
(b) √3R
(c) 2R
(d) 3R

Question 34:  The permeability of a paramagnetic substance is:

(a) very large
(b) small but more than unity
(c) less than unity
(d) negative

Answer (b) small but more than unity

Question 35:  Which of the following shows that the earth behaves as a magnet?

(a) Repulsion between like poles .
(b) Attraction between unlike poles
(c) Null points in the magnetic field of a bar magnet
(d) No existence of isolated magnetic poles

Answer (c) Null points in the magnetic field of a bar magnet

Question 36:  What is the angle of dip at the magnetic poles ?

(a) 30°
(b) 0°
(c) 45°
(d) None of these

Question 37:  Circular loop of radius 0.0157 m carries a current 2 A. The magnetic field at the centre of the loop is :

(a) 1.57 × 10-3Wb/m²
(b) 8.0 × 10-5 Wb/m²
(c) 2.0 × 10-3 Wb/m²
(d) 3.l4 × 10-1 Wb/m²

Answer (b) 8.0 × 10-5 Wb/m²

Question 38: The gyro-magnetic ratio of an electron in an H-atom, according to Bohr model, is

(a) independent of which orbit it is in.
(b) neutral
(c) positive
(d) increases with the quantum number n.

Answer (a) independent of which orbit it is in.

Question 39: A charge + q is sent through a magnetic field. The force acting on it is maximum w hen the angle between the direction of motion of the charged particle and the magnetic field :

(a) 0°
(b) 45°
(c) 90°
(d) 180°

Question 40:  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

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

Question 41:  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.

Answer (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 42:  The resistivity of a galvanometer is 60 division/amp. When a shunt is used, its sensitivity becomes 10 divisions/amp. If galvanometer is of resistance 20Ω, the value of shunt used is:

(a) 4Ω
(b) 5Ω
(c) 20Ω
(d) 20/7

Question 43:  Which device will have the least resistance?

(a) Ammeter of range 1A
(b) Ammeter of range 10 A
(c) Voltmeter of range 1 V
(d) Voltmeter of range 10 V

Answer (b) Ammeter of range 10 A

Question 44: A proton and an electron enter a region in which a magnetic field is suddenly switched on. The forces experienced by them are:

(a) equal and opposite.
(b) different in magnitude but in same direction.
(c) in the ratio of 1840.
(d) same in magnitude and direction.

Question 45:  When we double the radius of a coil keeping the current through it unchanged, what happens to the magnetic field directed along its axis at far off points?

(a) halved
(b) doubled
(d) remains unchanged

Question 46: The force between two parallel current carrying conductors is F. If the current in each conductor is doubled, then the force between them becomes :

(a) 4F
(b) 2F
(c) F

(d) F/4

Question 47:  Which of the following is not a unit of magnetic induction?

(a) gauss
(b) tesla
(c) oersted
(d) weber/metre²

Question 48:  The magnetic field of a given length of a ware for single turn coil at its centre is B. Then.its value for two turns of coil will be :

(a) B/4
(b) B/2
(c) 4B
(d) 2B

Question 49:   When charged particle enters-a uniform magnetic field, its K.E.

(a) remains constant
(b) increases
(c) decreases
(d) becomes zero

50. 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