Question

A source of monochromatic radiation of wavelength 400 nm provides 1000 J of energy in 10 seconds. When this radiation falls on the surface of sodium, $x\times {10}^{20}$ electrons are ejected per second. Assume that wavelength 400 nm is sufficient for ejection of electron from the surface of sodium metal. The value of x is . (Nearest integer)
$(h=6.626\times {10}^{-34}Js)$

Answer 1

$E=nh\nu =\frac{nhc}{\lambda }$

$1000=\frac{n\times 6.626\times {10}^{-34}\times 3\times {10}^8}{400\times {10}^{-3}}$

$\begin{array}{cc}n=20.122\times {10}^{20}& \text{photons incidented on metal surface in 10 seconds}\\ n=2.0122\times {10}^{20}& \text{photon incidented on metal surface in 1 second}\end{array}$

Since wavelength required for electron ejection is same as incident radiation, number of electrons ejected is equal to number of photon incidented.
Value of X = 2