IF an electron 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 field and v be velocity when it leaves the plates. Component of velocity parallel to the plates will remain unchanged. Hence `u cos alpha = v cos beta`
`:. (u)/(v) =(cos beta)/(cos alpha)`
`:. (((1)/(2)m u^(2)))/(((1)/(2) mv^(2)))= ((u)/(v))^(2) = ((cos beta)/(cos alpha))^(2)`