An electron moving with a uniform velocity along the positive `x`-direction enters a magnetic field directed along the positive `y`-direction. The force on the electron is directed along

Options

A. Along the positive Z-direction.
B. Along the negative Z-direction.
C. Along the positive Y-direction.
D. Along the negative Y-direction.

Answer

b

Explanation

Magnetic force on a charge is given by
`vec F = q vecv xx vec B`
`rArr vec F = (- e) ( v hat i) xx (B hat j) = - e v B hat k = ev B (- hat k)`
On the other hand, if we curl the fingers of our right hand from velocity vector towards the magnetic field vector, then our thumb will point along the Z-direction. But an electron is a negatively charged particle, so the direction of force becomes opposite, hence along the negative z-direction. Thus, option (b) is correct.