A small plate of a metal is placed at a distance of 2m from a monochromatic light source of wavelenght `4.8xx10^(-7)m` and power 1.0 Watt. The light falls normally on the plate. Find the number of photons striking the metal plate per square metre per second.

Options

A. `9.65 xx10^(18)`
B. `9.65 xx10^(17)`
C. `9.65 xx10^(16)`
D. `9.65 xx10^(15)`

Answer

A

Explanation

Energy of photon emitted `= hc//lamda` , the energy of light falling per second per unit are of a metal surface `= P//(4pir^2)`
`:.` No. of photons falling per second per unit area of metal surface `= P/(4pir^2) xxlamda/(hc)`
`= (20 xx 4.8 xx 10^(-7))/(4 xx 3.14 xx2^(2) xx 6.6 xx10^(-34)xx 3xx 10^(8))= 9.65 xx 10^(17)`