A very long straight wire carries a current I. At the instant when a charge `+Q` at point `P` has velocity `vecV`, as shown, the force on the charge is

Options

A. along Oy
B. opposite to Oy
C. along Ox
D. opposite to Ox.

Answer

A

Explanation

According to Fleming.s left hand rule, direction of force is along Oy axis which is perpendicular to wire.
`:.` Magnetic force, `vec(F) = e(vec(v) xx vec(B))`. Now, B due to I is acting inwards i.e., into the paper, v is alongOx.
`:. F= Q^(+) |(hat(i),hat(j),hat(k)),(v,0,0),(0,0,-B)| rArr F= Q^(+) [-hat(j)(-vB)+ 0]`
`:. vec(F) = +QvB hat(j)`, i.e. in Oy-direction