Question: Q. 1. Two charged particles traverse identical helical paths in a completely opposite sense in a uniform magnetic field $B=B_{0} \hat{k}$.
(a) They have equal $z$-components of momenta.
(b) They must have equal charges.
(c) They necessarily represent a particleantiparticle pair.
(d) The charge to mass ratio satisfy : $\left(\frac{e}{m}\right){1}+\left(\frac{e}{m}\right){2}=0$.
[NCERT Exemplar]
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Solution:
Ans. Correct option : (d)
Explanation : When charge/mass ratio of these two particles are same and charges on them are of opposite nature then the charged particles will traverse identical helical paths in a completely opposite sense.
i.e., $\quad:\left(\frac{e}{m}\right){1}+\left(\frac{e}{m}\right){2}=0$
