A small metal plate of work function `phi` is kept at a distance r from a singly ionised, fixed ion. A monochromatic light beam is incident on the metal plate and photoelectrons are emitted. Find maximum wavelength of the light beam so that some of that electrons may go round the ion along a circle.

Explanation

Electron is moving around the ion in a Circle of radius d.`1/(4piepsilon_(0))e^(2)/d^(2)=(mV^(2))/d, :. mV^(2)=1/(4piepsilon_(0))e^(2)/d`
`:.K.E=1/(8piepsilon_(0))e^(2)/d`....(1)
But `K.E_(max)=(hc)/lambda-W`......(2)
`:.lambda=(hc 8piepsilon_(0)d)/(de^(2)+8piepsilon_(0)dW)`