$ \Rightarrow $$\frac{{0.01}}{{10}} = \frac{5}{{50 + S}}$
$ \Rightarrow $ $S = \frac{{50}}{{999}} = 0.05\,\Omega $.
Assertion $(A)$ : In an uniform magnetic field, speed and energy remains the same for a moving charged particle.
Reason $(R)$ : Moving charged particle experiences magnetic force perpendicular to its direction of motion.