Two charged particles traverse identical helical paths in a completely opposite sense in a uniform magnetic field B = ${\mathrm{B}}_0\hat{\mathrm{k}}$.

1. They have equal z-components of momenta.

2. They must have equal charges.

3. They necessarily represent a particle-antiparticle pair.

4. The charge to mass ratio satisfy: $(\frac{e}{m}{)}_1+(\frac{e}{m}{)}_2=0$

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,
 

1. (b, c)

2. (a, d)

3. (b, d)

4. (c, d)

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,
 

1. (a, b, c)

2. (a, c, d)

3. (b, c, d)

4. (c, d)

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

(a) E = 0, B ≠ 0.
(b) E ≠ 0, B ≠ 0.
(c) E ≠ 0, B = 0.
(d) E = 0, B = 0.

1. (a, c)

2. (b, d)

3. (b, c, d)

4. (c, d)