A very large metal plate carries a charge of `Q=-1C`. The work function for the metal is `phi = 3eV` The plate is illuminated by a `60` watt light source with a wavelength `lambda` of `330nm`. How long does it take to completely discharge the plate? (Assume that every efficient photon ejects electron which is instantly removed from the sheet surface. (All photons ejected from light source fall normally on the metal plate) (`h=6.6 xx 10^(-34) m^2 kg//s`)

Options

A. 0.005 s
B. 0.025 s
C. 0.0625 s
D. 0.01

Explanation

The energy per photon is
`E_(lambda)=(hc)/(lambda)=(6.6xx10^(-34)m^(2)k g //sxx3xx10^(8) m//s)/(3.3xx10^(-7)m) 6xx10^(-19) J`
The time is to discharge the plate is given by total number of electrons divided by the rate of photons
`t=Q//exx(E_(lambda))/P=(6xx10^(-19)J)/(1.6xx10^(-19)xx60J//s) =0.0625 s`