In the following arrangement `y = 1.0 mm , d = 0.24 mm` and `D = 1.2 m`. The work function of the material of the emitter is `2.2 eV`. The stopping potential `V` needed to stop the photo current will be

Options

A. `0.9 V`
B. `0.5 V`
C. `0.4 V`
D. `0.1 V`

Answer

A

Explanation

As we know in Young's double slit experiment fringe width = separation between two consecutive fringe or dark fringes ` = b = (lambda D)/(d)`
Here `beta = 2 y rArr (lambda D)/( d) rArr lambda = ( 2yd)/(D)`
`rArr lambda = ( 2 xx 1 xx 10^(-3) xx 0.24 xx 10^(-3))/(1.2) = 4 xx 10^(-7) m = 4000 Å`
Energy of light incident on photo plate
`E ( eV) = (12375)/(4000) = 3.1 eV`
According to Einstein photoelectric equation ,
` E = W_(0) + eV_(0) rArr V_(0) = ((E - W_(0)))/(e) = (( 3 + 2.2 ))/( e) ev ~~ 0.9 V`