Moving Charges ...

Two charged particles traverse identical helical paths in a completely opposite sense in a uniform magnetic field \(B=B_0\hat k\).

Biot-Savart law indicates that the moving electrons (velocity v) produce a magnetic field B such that

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.

An electron is projected with uniform velocity along the axis of a current carrying long solenoid. Which of the following is true?

In a cyclotron, a charged particle

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 30° about an axis perpendicular to its plane is

(a) MB

(b) \(\sqrt3{MB\over2}\)

(c) \({MB\over2}\)

(d) Zero

The gyro-magnetic ratio of an electron in an H-atom, according to Bohr model, is

(a) independent of which orbit it is in

(b) negative

(c) positive

(d) increases with the quantum number n

Consider a wire carrying a steady current, I placed in a uniform magnetic field B perpendicular to its length. Consider the charges inside the wire. It is known that magnetic forces do no 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

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) \(\oint B.dl= m\mu_0I\)

(b) the value off \(\oint B.dl= +2\mu_0I\) 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

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 opposite face with velocity – v. At this instant,

(a) the electric forces on both the particles cause identical accelerations

(b) the magnetic forces on both the particles cause equal accelerations

(c) both particles gain or loose energy at the same rate

(d) the motion of the Centre of Mass (CM) is determined by B alone

A charged particle would continue to move with a constant velocity in a region wherein,

(a) E = 0, B \(\neq\) 0

(b) E \(\neq\) 0, B \(\neq\) 0

(c) E \(\neq\) 0, B = 0

(d) E = 0, B = 0