CBSE Class 12 Physics Moving Charges and Magnetism Worksheet Set B

CBSE Class 12 Physics Moving Charges and Magnetism Worksheet Set B

Question. Two charged particles traverse identical helical paths in a completely opposite sense in a uniform magnetic field 
B = B0k̂
(a) They have equal z-components of momenta
(b) They must have equal charges
(c) They necessarily represent a particle, anti-particle pair
(d) The charge to mass ratio satisfy (e/m)₁ + (e/m)₂ = 0

Answer: D

Question. Biot-Savart law indicates that the moving electrons (velocity v) produce a magnetic field B such that
(a) B is perpendicular of
(b) B is parallel to v
(c) it obeys inverse cube law
(d) it is along the line joining the electron and point of observationt.

Answer: A

Question. An alternating electric field, of frequency v, is applied across the dees (radius = R) of a cyclotron that is being used to accelerate protons (mass = m). The operating magnetic field (B) used in the cyclotron and the kinetic energy (K) of the proton beam, produced by it, are given by
(a) B = mv/e and K = 2mπ²ν²R²
(b) B = 2πmv/e and K = m²πνR²
(c) B = 2πmv/e and K = 2mπ²ν²R²
(d) B = mv/e and K = m²πνR²

Answer: C

Question. The magnetic field (dB) due to small element (dl) at a distance (r̅) r from element carrying current i, is 

Answer: D

Question. A 10eV electron is circulating in a plane at right angles to a uniform field at a magnetic induction 10^–4 Wb/m² (= 1.0 gauss). The orbital radius of the electron is
(a) 12 cm
(b) 16 cm
(c) 11 cm
(d) 18 cm

Answer: B

Question. The radius of motion of a charged particle oscillating in a magnetic field is
(a) mB/qv
(b) mv/qB
(c) mq/vB
(d) qv/mB

Answer: B

Question. A current loop in a magnetic field
(a) can be in equilibrium in one orientation
(b) can be in equilibrium in two orientations, both the equilibrium states are unstable
(c) can be in equilibrium in two orientations, one stable while the other is unstable
(d) experiences a torque whether the field is uniform or non-uniform in all orientations

Answer: C

Question. A magnetic needle suspended parallel to a magnetic field requires √3 J of work to turn it through 60°. The torque needed to maintain the needle in this position will be
(a) 2 √3J
(b) 3J
(c) √3J
(d) 3/2 J

Answer: B

Question. A current carrying circular loop of radius R is placed in the xy 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

Question. When a proton is released from rest in a room, it starts with an initial acceleration a₀ towards west. When it is projected towards north with a speed v₀ it moves with an initial acceleration 3a₀ towards west. The electric and magnetic fields in the room are respectively 

Answer: A

Question. A long straight wire carries a certain current and produces a magnetic field of 2 × 10^–4 weber/m2 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) Zero
(b) 3.2 N
(c) 3.2 × 10^–16 N
(d) 1.6 × 10^–16 N

Answer: C

Question. A circular coil ABCD carrying a current i is placed in a uniform magnetic field. If the magnetic force on the segment AB is F̅ , the force on the remaining segment BCDA is

(a) F̅
(b) -F̅
(c) 3 -F̅
(d) -3F̅

Answer: B

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. Two identical long conducting wires AOB and COD are placed at right angle to each other, with one above other such that ‘O’ is their common point for the two. The wires carry I₁ and I₂ currents respectively. Point ‘P’ is lying at distance ‘d’ from ‘O’ along a direction perpendicular to the plane containing the wires. The magnetic field at the point ‘P’ will be :
(a) μ₀/2πd(I₁/I₂)
(b) μ₀/2πd(I₁+I₂)
(c) μ₀/2πd(I₁²+I₂²)
(d) μ₀/2πd(I₁2+I₂²)1/2

Answer: D

Question. An electron moving in a circular orbit of radius r makes n rotations per second. The magnetic field produced at the centre has magnitude:
(a) Zero
(b) μ₀n²e/r
(c) μ₀ne/2r
(d) μ₀ne/2πr

Answer: C

Question. Magnetic effect of current was discovered by
(a) Faraday
(b) Oersted
(c) Kirchhoff
(d) Joule

Answer: B

Question. Electron move at right angle to a magnetic field of 1.5 × 10^–2 tesla with speed of 6 × 107 m/s. If the specific charge of the electron is 1.7 × 10¹¹ C/kg. The radius of circular path will be
(a) 3.31 cm
(b) 4.31cm
(c) 1.31 cm
(d) 2.35 cm

Answer: D

Question. A wire carrying current I has the shape as shown in adjoining figure. Linear parts of the wire are very long and parallel to X-axis while semicircular portion of radius R is lying in Y-Z plane. Magnetic field at point O is :
(a) B̅ = -μ0/4π I/R (μî x 2k̂)
(b) B̅ = -μ0/4π I/R (πî + 2k̂)
(c) B̅ = μ0/4π I/R (πî - 2k̂)
(d) B̅ = μ0/4π I/R (πî + 2k̂)

Answer: B

Question. Charge q is uniformly spread on a thin ring of radius R. The ring rotates about its axis with a uniform frequency f Hz.
The magnitude of magnetic induction at the centre of the ring is
(a) μ₀qf/2R
(b) μ₀q/2fR
(c) μ₀q/2πfR
(d) μ₀qf/2πR

Answer: A

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

Directions for : Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer (ONLY ONE option is correct ) from the following.
(a) Statement -1 is false, Statement-2 is true
(b) Statement -1 is true, Statement-2 is true; Statement -2 is a correct explanation for Statement-1
(c) Statement -1 is true, Statement-2 is true; Statement -2 is not a correct explanation for Statement-1
(d) Statement -1 is true, Statement-2 is false

Question. Statement 1 : A cyclotron cannot accelerate neutrons.
Statement 2 : Neutrons are neutral.

Answer: B

Question. Statement 1 : The magnetic field at the centre of the circular coil in the following figure due to the currents I₁ and I₂ is zero.

Statement 2 : I₁ = I₂ implies that the fields due to the current I₁ and I₂ will be balanced.

Answer: D

Question. Statement 1 : If the current in a solenoid is reversed in direction while keeping the same magnitude, the magnetic field energy stored in the solenoid decreases.
Statement 2 : Magnetic field energy density is proportional to square of current.

Answer: A

Question. Statement 1 : If a charged particle is released from rest in a region of uniform electric and magnetic fields parallel to each other, it will move in a straight line.
Statement 2 : The electric field exerts no force on the particle but the magnetic field does.

Answer: C
 

              Very Short Answer

Q1)       What is Bohr magnetron?

Q2)       What is gyromagnetic ratio?

Q3)       Define voltage sensitivity?

Q4)       What is Bohr quantisation condition?

Q5)       Define amperian loop?

              Short Answer

Q6)       What do you mean by magnetic confinement?

Q7)       What do you mean by spin magnetic moment?

Q8)       What do you mean by the right hand thumb rule?

Q9)       How Ampere’s Circuital law is used?

Q10)     What do you mean by the Ampere’s law?

              Long Answer

Q11)     Write short note on toroid?

Q12)     Explain about the moving coil galvanometer?

Q13)     Explain about the magnetic dipole?

Q14)    Write short note on the solenoid?

Q15)     Write short note on Roget’s Spiral for attraction between parallel currents?