A non-relativistic charge q of mass m originates at a point A lying on x-axis and moves with velocity v at an angle to the x-axis. A screen is located at a distance l from A. Find the distance r from the x-axis to the point on the screen into which the charge strikes.

Explanation

Time taken by particle to reach the screen: `t=l/(vcos alpha)`

Radius of helical path : `R=(mvsin alpha)/(qB)`
angle rotated in time `t: theta=omegat=(qB)/mt`
Required distance:
`r=2R sin ((theta)/2)=(2mvsin alpha)/(qB) sin((qB)/(2m) l/(v cos alpha))`