Class 12 Physics Chapter 4 Moving Charges and Magnetism MCQ Questions

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Class 12 Moving Charges and Magnetism MCQ Questions with answers

Class 12 Physics MCQ with answers are given here to Moving Charges and Magnetism. These MCQs are based on the latest CBSE board syllabus and relate to the latest Class 12 Physics syllabus. By Solving these Class 12 MCQs, you will be able to analyze all of the concepts quickly in the chapter and get ready for the Class 12 Annual exam.

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Question 1. 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

Question 2. 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

Question 3. A long solenoid carrying a current produces a magnetic field B along its axis. If the current is doubled and the number of turns per cm is halved, the new value of the magnetic field is
(a) B/2
(b) B
(c) 2 B
(d) 4 B

Question 4. 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°.

Question 5. 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 

Question 6. 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.

Question 7. 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.

Question 8. 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

Question 9. 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

Question 10. 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 

Question 11. 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.

Question 12. 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 

Question 13. A charged particle enters a magnetic field H with its initial velocity making an angle of 45° with H.
Then the path of the particle will be: 
(a) circle
(b) helical
(c) a straight line
(d) a circle

Question 14. An electron moving with kinetic energy 6.6´10-14 J enters in a magnetic field of 4´10-3T at right angles to it. The radius of its circular path will be nearest to : 
(a) 100 cm
(b) 75 cm
(c) 25 cm
(d) 50 cm

Question 15. 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 

Question 16. 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 

Question 17. A galvanometer of resistance, G, is shunted by a resistance S ohm. To keep the main current in the circuit unchanged, the resistance to be put in series with the galvanometer is
(a) G /(S +G)
(b) S2 /(S +G)
(c) SG /(S +G)
(d) G2/ (S +G )

Question 18. 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.

Question 19. 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

Question 20. 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 T 

Question 21. 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 

Question 22. 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 W
(b) 1800 W
(c) 500 W
(d) 1000 W. 

Question 23. 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

Question 24. 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 

Question 25. 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

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Question 26. 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.

Question 27. 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.

Question 28. 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

Question 29. The magnetic force acting on a charged particle of charge –2 mC 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. 

Question 30. 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.

Question 31. 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

Question 32. Electron of mass m and charge q is travelling with a speed along a circular path of radius r at right angles to a uniform magnetic field of intensity B. If the speed of the electron is doubled and the magnetic field is halved the resulting path would have a radius 
(a) 2 r
(b) 4 r
(c) r /4
(d) r/2

Question 33. The magnetic field due to a square loop of side a carrying a current I at its centre is 
(a) μ₀i / 2a
(b) μ₀i / √2Πa
(c) μ₀i / 2Πa
(d) √2μ0i /Πa

Question 34. 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

Question 35. 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

Question 36. A long solenoid of 50 cm length having 100 turns carries a current of 2.5 A. The magnetic field at the centre of the solenoid is (m0 = 4p × 10^–7 T m A^–1)
(a) 6.28 × 10^–4 T
(b) 3.14 × 10^–4 T
(c) 6.28 × 10^–5 T
(d) 3.14 × 10^–5 T 

Question 37. 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. 

Question 38. 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. 

Question 39. Two toroids 1 and 2 have total number of turns 200 and 100 respectively with average radii 40 cm and 20 cm respectively. If they carry same current i, the radio of the magnetic fields along the two loops is
(a) 1 : 1
(b) 4 : 1
(c) 2 : 1
(d) 1 : 2

Question 40. Two concentric circular coils of ten turns each are situated in the same plane. Their radii are 20 and 40 cm and they carry respectively 0.2 and 0.4 ampere current in opposite direction. The magnetic field in weber/m2 at the centre is
(a) μ₀/80
(b) 7μ₀/80
(c) (5/4) μ₀
(d) zero

Question 41. 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

Question 42. A uniform electric field and a uniform magnetic field exist in a region in the same direction. An electron is projected with velocity pointed in the same direction. The electron will
(a) turn to its right
(b) turn to its left
(c) keep moving in the same direction but its speed will increase
(d) keep moving in the same direction but its speed will decrease

Question 43. Energy in a current carrying coil is stored in the form of
(a) electric field
(b) magnetic field
(c) dielectric strength
(d) heat

Question 44. A cathode ray beam is bent in a circle of radius 2 cm by a magnetic induction 4.5 × 10^–3 weber/m². The velocity of electron is
(a) 3.43 × 10⁷ m/s
(b) 5.37 × 10⁷ m/s
(c) 1.23 × 10⁷ m/s
(d) 1.58 × 10⁷ m/s

Question 45. Protons and a-particles of equal momenta enter a uniform magnetic field normally. The radii of their orbits will have the ratio.
(a) 1
(b) 2
(c) 0.5
(d) 4

Question 46. A current of I ampere flows along an infinitely long straight thin walled hollow metallic cylinder of radius r. The magnetic field at any point inside the cylinder at a distance x from the axis of the cylinder is

(a)

(b)

(c)

(d) Zero

Question 47. Under the influence of a uniform magnetic field a charged particle is moving in a circle of radius R with constant speed v. The time period of the motion
(a) depends on both R and v
(b) is independent of both R and v
(c) depends on R and not v
(d) depends on v and not on R

Question 48. A wire of length L metre carrying a current I ampere is bent in the form of a circle. Its magnitude of magnetic moment will be
(a) IL/4π
(b) I²L²/4π
(c) IL²/4π
(d) IL²/8π

Question 49. A current of 3 A is flowing in a linear conductor having a length of 40 cm. The conductor is placed in a magnetic field of strength 500 gauss and makes an angle of 30º with the direction of the field. It experiences a force of magnitude
(a) 3 × 10^–4 N
(b) 3 × 10^–2 N
(c) 3 × 10² N
(d) 3 × 10⁴ N

Question 50. 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

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