Question

Light of wavelength $5000\stackrel{\circ }{A}$ is falling on a photo sensitive surface. If the surface has received ${10}^{-7}$J of energy, then the number of photons falling on the surface will be

• A. $5\times {10}^{11}$
• B. $2.5\times {10}^{11}$
• C. $9\times {10}^{11}$
• D. $1\times {10}^{11}$

Answer 1

The correct option is B $2.5\times {10}^{11}$

Energy received $E=\frac{nhc}{\lambda }\Rightarrow E=n\left(\frac{12400}{\lambda }\right)eV\Rightarrow {10}^{-7}=n\times \frac{12400}{5000}\times 1.6\times {10}^{-19}\Rightarrow n=\frac{5}{12.4\times 1.6}\times {10}^{12}\Rightarrow n=2.5\times {10}^{11}$