IF an electorn enters into a space between the plates of a parallel plate capacitor at an an angle `alpha` with the plates an leaves at an angle `beta` to the plates find the ratio of its kinetic energy while entering the capacitor of that while leaving.

Explanation

Let `u` be the velocity of electron while entering the filed and `v` be the velocity when it leaves the plates.Compound of velocity parallel to the plates will remain unchanged.
Hence `u cos alpha=u cos beta:.(u)/(v)=(cos beta)/(cos alpha)`
`therefore (((1)/(2)m u^(2)))/(((1)/(2)mv^(2)))=((u)/(v))^(2)=((cosbeta)/(cosalpha))^(2)`