Question

A beam of light has three wavelengths $4144\dot{A},4972\dot{A},6216\dot{A}$ with a total intensity of $3.6\times {10}^{–3}W/m^2$ equally distributed amongst the three wavelengths. The beam falls normally on $1c{m}^2$ of a clean metallic surface of work function $2.3eV$. The number of photoelectrons liberated in $2$ s is closest to (assume every capable photon ejects an electron)

• A. $8\times {10}^{11}$
• B. $11\times {10}^{11}$
• C. $5\times {10}^{11}$
• D. $2\times {10}^{11}$

Answer 1

The correct option is B $11\times {10}^{11}$

$N=\frac{IAt({\lambda }_1+{\lambda }_2)}{3hc}$

Only two of the wavelengths are capable of ejecting $e^{–}$.