Define the distance of closest approach. An `alpha`-particle of kinetic enegy `'K'` is bombarded on a thin gold foil. The distance of the closest approach is `'r'` . What will be the distance of closest approach for an `alpha`-particle of double the kinetic energy ?

Explanation

Distance of closest approach is defined as the minimum distance between the charged particle and the nucleus at which initial kinetic energy of the particle is equal to electrostatic potential energy
for `alpha` particle, `(K Ze (2e))/r=1/2mv_(alpha)^(2)`
`r prop 1/(K.E.)`
`therefore` r will be halved.