NEET Physics Moving Charges and Magnetism MCQs Set A

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. 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

Question. 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 continue to move with uniform velocity along the axis of the solenoid
(b) The electron will experience a force at 45° to the axis and hence execute a helical path
(c) The electron path will be circular about the axis
(d) The electron will be accelerated along the axis

Answer: A

Question. In a cyclotron, a charged particle
(a) undergoes acceleration all the time
(b) speeds up between the dees because of the magnetic field
(c) speeds up in a dees
(d) slows down within a dee and speeds up between dees

Answer: A

Question.  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) four times
(b) double
(c) three times
(d) one-fourth

Answer: A

Question.  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) 1 MeV
(b) 0.5 MeV
(c) 1.5 MeV
(d) 4 MeV

Answer: A

Question. 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%

Answer: A

Question. 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 not a correct explanation for assertion
(b) Assertion is correct, reason is incorrect
(c) Assertion is incorrect, reason is correct.
(d) Assertion is correct, reason is correct; reason is a correct explanation for assertion

Answer: A

Question.  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) 100 keV
(b) 50 keV
(c) 25 keV
(d) 200 keV

Answer: A

Question.  A coil of circular cross-section having 1000 turns and 4 cm² face area is placed with its axis parallel to a magnetic field which decreases by 10^–2 Wb m^–2 in 0.01 s. The e.m.f. induced in the coil is:
(a) 400 mV
(b) 4 mV
(c) 200 mV
(d) 0.4 mV

Answer: A

Question.  A charged particle moves through a magnetic field perpendicular to its direction. Then
(a) the momentum changes but the kinetic energy is constant
(b) both momentum and kinetic energy of the particle are not constant
(c) both momentum and kinetic energy of the particle are constant
(d) kinetic energy changes but the momentum is constant

Answer: A

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) 11.32 A
(b) 14.76 A
(c) 5.98 A
(d) 7.14 A

Answer: A

Question. Assertion: The frequency of circular motion of a charged particle in cyclotron is independent of the mass of the particle.
Reason: Greater the mass of the particle less will be the frequency of the particle.
(a) Assertion is incorrect, reason is correct
(b) Assertion is correct, reason is incorrect
(c) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(d) Assertion is correct, reason is correct; reason is a correct explanation for assertion.

Answer: A

Question.  A steady current I flows down a hollow cylindrical tube of radius a and is uniformly distributed around the tube. Let r be the distance from the axis of symmetry of the tube to a given point. What is the magnitiude of the magnetic field B at a point inside the tube?
(a) 0
(b) 2 I/r c
(c) 2 I r/a²c
(d) None of these

Answer: A

Question.  The length of a solenoid is 0.4 m and the number turns in it is 500. A current of 3 amp, is flowing in it. In a small coil of radius 0.01 m and number of turns 10, a current of 0.4 amp. is flowing. The torque necessary to keep the axis of this coil perpendicular to the axis of solenoid will be
(a) 5.92 × 10^–6 N-m
(b) 5.92 × 10^–4 N-m
(c) 5.92 × 10^–4 dyne-cm
(d) 5.92 × 10^–6 dyne-cm

Answer: A