A region has uniform electric and magnetic fields along the positive `x`-direction. An electron is fired from the origin at an angle `theta( lt 90^(@))` with the x-axis. It will
(i) move along a helical path of increasing pitch
(ii) move along a helical path of decreasing pitch initially
(iii) return to the `yz` plane at some time
(iv) come to rest momentarily at some position

Options

A. (i), (ii)
B. (ii), (iv)
C. (ii), (iii)
D. (i), (iv)

Answer

C

Explanation

Along x-axis, due to electric force, particle moves with decreasing speed hence pitch is decreasing. After sometime, velocity becomes zero and particle moves along `-ve` x-axis.