CBSE Class 12 Physics Moving Charges and Magnetism MCQs Set C

Question. 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

Answer : B

Question. 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.

Answer : B

Question. 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

Answer : D

Question. 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

Answer : B

Question. 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

Answer : D

Question. 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

Answer : B

Question. 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

Answer : A

Question. 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.

Answer : D

Question. According to Biot Savart’s law, the magnetic field produced by a current carrying conductor is perpendicular to the plane containing:
(a) r
(b) Idl
(c) the conductor
(d) r and Idl

Answer : D

Question. A horizontal overhead power line carries a current of 90 A in east to west direction. What are the magnitude and direction of the magnetic field due to this current 1.5 m below the line?
(a) 1.2 x 10-5T perpendicularly outwards to the plane of paper
(b) 1.9 x 10-5T perpendicularly outwards to the plane of paper
(c) 2.6x 10-5T perpendicularly inwards to the plane of paper
(d)2.6 x 10-5T perpendicularly outwards to the plane of paper

Answer : A

Question. If the force per unit length between two long straight wires carrying currents 4 A and 6 A is 1.6 X 10-4 N/m, then the distance between the wires is
(a) 5 cm
(b) 3 cm
(c) 3 m
(d) 1 cm

Answer : B

Question. Which of the following is an incorrect formula for magnetic force experienced by a conductor in magnetic field? Options are not readable due to notation
(a) I (LXB)
(b) (jAL) X B
(c) nALqvd X B
(d) I (jL X B)

Answer : D

Question. Just as static charges produce electric field, moving charges produce:
(a) Electric field only
(b) magnetic field only
(c) Both electric and magnetic fields
(d) drift velocity

Answer : C

Question. Calculate the force experienced by the loop in the given figure:

(a) 17.8 X 10^-4 N (Attractive)
(b) 7.8 X 10^-4 N (Attractive)
(c) 17.8 X 10^-6 N (Attractive)
(d) 7.8 X 10^-4 N (Repulsive)

Answer : B

Question. When a rectangular coil carrying current is suspended in magnetic field, then net force experienced by the coil is:
(a) nIBAsinφ
(b) M X B
(c) zero
(d) nIBA

Answer : C

Question. The magnetic field in the outside region of the given figure is :

(a) μ0nI
(b) μ0NI
(c) infinite
(d) zero

Answer : D

Question. 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 )

Answer : D

Question. 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 

Answer : B

Question. 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

Answer : B

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. 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

Answer : B

Question. If a straight current carrying wire is suspended horizontally in mid-air by a uniform magnetic field, then what could be the possible reason for it?
(a) The gravitational force is balanced by electric field produced by wire.
(b) The external magnetic field is balanced by magnetic field due to conductor.
(c) The magnetic field produced by conductor is balanced by magnetic field of Earth.
(d) The gravitational force on the conductor is balanced by external magnetic field.

Answer : D

Question. As per Ampere’s circuital law, the magnetic field at every point on a circle of radius r, HAVING current carrying wire along the axis, possesses ____________symmetry.
(a) spherical
(b) Linear
(c) cylindrical
(d) none of these

Answer : C

Question. A galvanometer cannot be used as such as an ammeter because
(a) it has low resistance
(b) it has low sensitivity
(c) it has high resistance
(d) it is not well calibrated always.

Answer : C

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. 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.

Answer : B

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. 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

Answer : B

Question. 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.

Answer : B

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 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

Answer : D

Question. 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

Answer : B