A silver of radius `4.8 cm` is suspended by a thread in the vacuum chamber . `UV` light of wavelength `200 nm` is incident on the ball for some times during which a total energy of `1 xx 10^(-7) J` falls on the surface . Assuming on an average one out of `1000 photons incident is able to eject electron. The potential on sphere will be

Options

A. 1 V
B. 2 V
C. 3 V
D. Zero

Answer

C

Explanation

No. of photon `=(Elamda)/(hc) = (1 xx10^(-7)xx200 xx10^(-9))/(6.6 xx10^(-34) xx3 xx10^8) = 10^(11)`
No. of electrons ejected = `10^(11)/10^3 =10^8`
`V=q/(4piepsilon_0r)=(10^8xx1.6 xx10^(-19)xx9 xx10^9)/(4.8 xx10^(-2))=3V`