CBSE Class 12 Physics Moving Charges and Magnetism MCQs Set B

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

Answer : 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

Answer : B

Question. 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

Answer : B

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

Answer : C

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

Answer : A

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

Answer : 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

Answer : 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

Answer : D

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 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

Answer : D

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

Answer : B

Question. 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

Answer : D

Question. In definition of 1 A, the force between two very long, straight, parallel conductors of negligible cross-section, placed 1 m apart in vacuum is
(a) 2 X 10^-7 N
(b) 0.2 X 10 N
(c) 20 X 10 N
(d) None of the above

Answer : D

Question. ‘Parallel current CARRYING WIRES__________ and antiparallel current CARRYING WIRES ____________.
(a) attract, repel
(b) repel,attract
(c) attract, attract
(d) repel,repel

Answer : A

Question. If magnetic field inside a solenoid is 15 T, then what will be the approximate magnetic field near its one end?
(a) 30 T
(b) 7.5 T
(c) 15 T
(d) 0

Answer : B

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

Answer : B

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°.

Answer : D

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.

Answer : B

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

Answer : B

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.

Answer : 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) 3.15 × 10^–5 T

Answer : A

Question. 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

Answer : A

Question. 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

Answer : A

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.

Answer : A

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

Answer : A

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

Answer : 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

Answer : 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

Answer : D

Question. 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

Answer : B

Question. 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

Answer : C

Question. The value of gyromagnetic ratio, μ/𝑙 = 𝑒/2𝑚’ for an electron is:
(a) 6.6 X 10^-34 C/kg
(b) 8.8 X 10¹⁰ C/Kg
(c) 8.85 X 10¹² C/kg
(d) 1.6 X 10^-19 C/kg

Answer : B

Question. The magnetic force acting on a charged particle having charge -3μC in a magnetic field of 2 T acting in y direction, when the particle velocity is (2𝑖̂ + 3𝑗̂) X 10⁶ m/s is
(a) 12 N in -z direction
(b) 12 N in y direction
(c) 12 N in z direction
(d) 18 N in -z direction.

Answer : A

Assertion And Reason:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true and 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: If an electron and proton move in a uniform magnetic field with same speed in perpendicular direction, then they will experience same force (IN MAGNITUDE)
Reason: These particles have same charges.

Answer : C

Question. Assertion: The range of ‘galvanometer converted into an ammeter’ can be increased by reducing the value of shunt.
Reason: Shunt is connected in parallel TO galvanometer.

Answer : A