
Time taken by the electron to cross will be, t=vx1=21s.
Acceleration of the electron along y axis
ag=mF=mEe=e8m×me=8ms−2
vy of the electron when it has crossed the capacitor will be,
vy=ayt=8×21=4ms−1
Therefore,
tanθ=vxvy=24=2⇒θ=tan−1(2)