Question

An alpha particle is projected vertically upward with a speed of $3.0\times {10}^{4}km$ $s^{-1}$ in a region where a magnetic field of magnitude $1.0T$ exists in the direction south to north. Find the magnetic force that acts on the $\alpha$ particle.

Answer 1

Velocity $\overrightarrow{V}$ is upward and field $\overrightarrow{B}$ is towards south to north so $\overrightarrow{V}\times \overrightarrow{B}$ will be towars west by $right$ $hand$ screw rule and thus force $\overrightarrow{F}=q\overrightarrow{V}\times \overrightarrow{B}$ on $\alpha$ particle will be towards $west$.

Its value will be $F=2eVB=9.6\times {10}^{-12}N$ as for alpha particle $q=2e=3.2\times {10}^{-19}C$ and $V=3\times {10}^{7}m/s$ and $B=1.0T$