In a photocell bi chromatic light of wave length `2480 A^(0) ` and `6000 Aoverset(0)` are incident on a cathode whose workfunction is `4.8eV`.If a uniform magnetic field of `3xx10^(-5) T` exists parallel to the plate, find the radius of the circular path described by the photoelectron. (mass of electron is `9xx10^(-31)kg`)

Explanation

`E_(1)=12400/lambda_(1)=12400/2480=5eV, E_(2)=12400/lambda_(2)=12400/6000=2.06eV,`
As `E_(2) lt W_(0)` and `E_(1) lt W_(0)`, photo electric emission is possible only with `lambda_(1)`.
Maximum `K.E` of emitted photo electrons
`K=E_(1) - W_(0)=0.2eV`
Photo electrons experience magnetic force and move along a circular path of radius
`r=(mnu)/(Bq)=sqrt(2mK)/(Bq) rArr=5cm`.