A plane wave front of light is incident on a plane mirror. Intensity is maximum at P when

Options

A. `costheta=(lamda)/(2d)`
B. `costheta=(3lamda)/(4d)`
C. `sectheta-costheta=(3lamda)/(4d)`
D. `sectheta-costheta=(lamda)/(2d)`

Answer

B

Explanation

`BP=(MP)/(costheta)`
`AB=BPcos2theta=(MP)/(costheta)cos2theta`
`AB+BP=nlamda+(lamda)/(2)`
`(d cos2theta)/(costheta)+(d)/(costheta)=(d)/(costheta)(2cos^(2)theta-1+1)=2dcostheta=nlamda+(lamda)/(2)` for `n=1,costheta=(3lamda)/(4d)`