A uniform electric field E is created between two parallel, charged plates as shown in figure. An electron enters the field symmetrically between the plates with a speed v' . The length of each plate is d. Find the minimum value of v' , so that electron will not strike with the plate?

The acceleration of the electron is a=eEm in the upward direction. The horizontal velocity remains v0 as there is no acceleration in this direction. Thus, the time taken in crossing the field is: t=lv0 The upward component of the velocity of the electron as it emerges from the field region is: vy=at=eElmv0 The horizontal component of the velocity remains vx=v0 The angle θ made by the resultant velocity with the original direction is given by: tanθ=vyvx Thus, the electron deviates by an angle: θ=tan−1eElmv02