An electron is launched with velocity `vec v` in a uniform magnetic field `vec B.` The angle `theta` between `vec v and vec B` lies between 0 and `pi /2`. Its velocity vector `vec v` returns to its initial value in a time interval of

Options

A. `(2pi m)/(eB)`
B. `(2xx2pi m)/(eB)`
C. `(pi m)/(eB)`
D. depends upon between `vec v and vec B`

Answer

A

Explanation

Time interval in which `vecv` returns to its initial value is
same as time period of the particle, hence the required time
`=(2pim)/(eB)`