Question

in an experimental set up to study the photoelectric effect a point soure fo light of power `3.2xx10^(-3)` W was taken. The source can emit monoenergetic photons of energy 5eV and is located at a distance of 0.8 m from the centre of a stationary metallic sphere of work-function 3.0 eV. The radius of the sphere is `r = 8..10^(-3)` m. The efficiency of photoelectric emission is one for every `10^6` incident photons. Based on the information given above answer the questions given below. (Assume that the sphere is isolated and photoelectrons are instantly swepts away after the emission).
de-Broglie wavelength of the fastest moving photoelectron is
A. `6.63 Å`
B. `8.69 Å`
C. `2 Å`
D. `5.26 Å`

Answer 1

Correct Answer - B
`K_(max) = E -W = 2eV
`lambda = (sqrt(150)/(KE(in eV)), for an electron
`=sqrt(150)/(2) ~~8.6 Å`