A flashlight of intensity 9 W/`cm^(2)` illuminates a perfectly reflective surface of area `300cm^(2)`. The average force exerted on the surface due to the incident light photons is

Options

A. 0N
B. `14muN`
C. `18muN`
D. `12muN`

Answer

C

Explanation

Given intersity of flash light, `I=9W//cm^(2)`
`9xx10^(4)W//m^(2)`
Area, `A=300cm^(2)=3xx10^(-2)m^(2)`
`:.` Radiation pressure due to incident light photon, `p=(2I)/(c)=(2xx9xx10^(4))/(3xx10^(8))`
`("":'` c= speed of light `=3.0xx10^(8)m//s`)
`p=6xx10^(-4)N//m^(2)`
Average force exerted on the surface,
`F=pxxA`
`=6xx10^(-4)xx3xx10^(-2)`
`=18xx10^(-6)N=18muN`