An electron is moving along positive x-axis. To get it moving on an anticlockwise circular path in x-y plane, a magnetic field is applied

Options

A. along positive y-axis
B. along positive z-axis
C. along negative y-axis
D. along negative z-axis

Answer

b

Explanation

For the particle to move along anticlockwise path, force
should be along `hatj`. Velocity is along `hati`.
Now, `vecF_m=-e(vecVxxvecB)`
In terms of unit vectors only,
`hatj=-(hatixxhat?) or hatj=hat?xxhati`
Clearly, `hat? is hatk.`