15. Two metal plates are connected to a battery and a current meter. When a light beam with tunable energy E is shined on one of the plates, the values read by the current meter is plotted as a function of E. E0 corresponds to the photon density of 10¹²cm^-3and the photon wavelength of 200 nm. When the incident photon wavelength is increased to 400 nm, what is the photon density to obtain the current value of 5 μA?
(A)2✖1012 cm^-3
(B)4✖10¹² cm^-3
(C)8✖10₂₂cm^-3
(D)10^12-3

(E)None of the above