Two charged particles $A$ and $B$,each of charge $+e$ and masses $12 \, amu$ and $13 \, amu$ respectively,follow a circular trajectory in chamber $X$ after passing through a velocity selector as shown in the figure. Both particles enter the velocity selector with a speed of $1.5 \times 10^6 \, ms^{-1}$. $A$ uniform magnetic field of strength $1.0 \, T$ is maintained within the chamber $X$ and in the velocity selector,directed into the plane ($-z$ direction).

• A
  Electric field across the conducting plate of the velocity selector is $-10^6 \, NC^{-1} \hat{i}$.
• B
  Electric field across the conducting plate of the velocity selector is $10^6 \, NC^{-1} \hat{i}$.
• C
  The ratio $r_A / r_B$ of the radii of the circular paths for the two particles is $12/13$.
• D
  The ratio $r_A / r_B$ of the radii of the circular paths for the two particles is $13/12$.