An ionized gas contains both positive and negative ions . If it is subjected simultaneously to an electric field along the ` +x` - direction and a magnetic field along the ` +y` - direction and the negative ions towardws `-y` - direction

Options

A. positive ions defect towards `+y` directionand negative ions towards `-y` direction
B. all ions deflect towards `+y` direction
C. all ions deflect towards `-y` direction
D. positive ions deflect towards `-y` direction and negative ions towards `+y` direction.

Answer

C

Explanation

If ion is positive then, it will acquire velocity in `(+ve)` x direction and hence magnetic force will act in `-y` direction `F_(M)=q(vec(v)xxvec(B))` for `(-)` ion. It will acquire velocity in `-x` direction due to electric field and hence magnetic force will act ion `-y` direction because charge is negative . Hence in both the case ions will deflect in `(-ve)` y direction.