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Practice each question, then open the answer or worked solution.
Two charged particles traverse identical helical paths in an opposite sense in a uniform magnetic field
a) they have equal z-components of momenta
b) they must have equal charges
c) they necessarily represent a particle-antiparticle pair
d) the charge to mass ratio satisfy: (e/m)1 + (e/m)2 = 0
d) the charge to mass ratio satisfy: (e/m)1 + (e/m)2 = 0
Biot-Savart law indicates that the moving electrons produce a magnetic field B such that
a) B ┴ v
b) B ‖ v
c) it obeys the inverse cube law
d) it is along the line joining the electrons and the point of observation
a) B ┴ v
A current circular loop of radius R is placed in the x-y plane with the centre at the origin. Half of the lop with x > 0 is now bent so that it now lies in the y-z plane.
a) the magnitude of the 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
a) the magnitude of the magnetic moment now diminishes
An electron is projected with uniform velocity along the axis of a current-carrying long solenoid. Which of the following is true?
d) the electron will continue to move with uniform velocity along the axis of the solenoid
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 dee
d) slows down within a dee and speeds up between dees
a) undergoes acceleration all the time
A circular current loop of magnetic moment M is in an arbitrary orientation in an external magnetic field B. The work done to rotate the loop by 30o about an axis perpendicular to its plane is
a) MB
b) √3 MB/2
c) MB/2
d) zero
d) zero
Multiple Choice Questions IIThe gyro-magnetic ratio of an electron in an H-atom, according to the Bohr model, is
a) independent of which orbit it is in
b) negative
Consider a wire carrying a steady current, I placed un a uniform magnetic field B perpendicular to its length. Consider the charges inside the wire. It is known that magnetic forces do not work. This implies that
a) motion of charges inside the conductor is unaffected by B since they do not absorb energy
b) some charges inside the wire move to the surface as a result of B
c) if the wire moves under the influence of B, no work is done by the force
d) if the wire moves under the influence of B, no work is done by the magnetic force on the ions, assumed fixed within the wire
b) some charges inside the wire move to the surface as a result of B
d) if the wire moves under the influence of B, no work is done by the magnetic force on the ions, assumed fixed within the wire
Two identical current-carrying coaxial loops carry current I in an opposite sense. A simple Amperian loop passes through both of them once. Calling the loop as C,
a)
b) the value of
is independent of sense of C
c) there may be a point on C where B and dl are perpendicular
d) B vanishes everywhere on C
b) the value of
is independent of sense of C
c) there may be a point on C where B and dl are perpendicular
A cubical region of space is filled with some uniform electric and magnetic fields. An electron enters the cube across one of its faces with velocity v, and a positron enters via the opposite face with velocity –v. At this instant,
a) the electric forces on both particles cause identical acceleration
b) the magnetic forces on both particles cause equal acceleration
c) both particles gain or lose energy at the same rate
d) the motion of the centre of mass (CM) is determined by B alone
b) the magnetic forces on both the particles cause equal acceleration
c) both particles gain or lose energy at the same rate
d) the motion of the centre of mass (CM) is determined by B alone