Let `I_(0)` be the intensity of polarised light after passing through the first polariser `P_(1)`,. Then the intensity of light after passing through second polariser `P_(2)` will be `I=I_(0)cos^(2)theta`
Where `theta` is the angle between pass axes `P_1 and P_2,”since “P_1 and P_2` are crossed the angle between the pass axes of `P_2 and P_3 “will be ” (pi/2-theta)`
Hence the intensity of light emerging from `P_3` will be
`I=I_(0)cos^(2)theta.cos^(2) “”(pi/2-theta)`
`=I_(0)cos^(2)theta.sin^(2)theta`
`I=I_(0)/4sin^(2)2theta`
`therefore` The transmitted intensity will be maximum when `theta=(pi)/(4)`

Let `I_(0)` be the intensity of polarised light after passing through the first polariser `P_1` Then the intensity of light after passing through second polariser `P_2` will be `I =I_(0)cos^(2)e,` where `theta` is the angle between pass axes of `P_1 and P_2.` Since `P_1 and P_3` are crossed the angle between the pass axes of P, and `P_3` will be `(pi//2 -theta)`. Hence the intensity of light emerging from `P_3` will be
`I=I_(0)cos^T(2)thetacos^(2)((pi)/(2)-theta)`
`=I_(0)cos^(2) thetasin^(2)theta=(I_(0)//4)sin^(2)2theta`
Therefore, the transmitted intensity will be maximum when `theta= lambda//4.`

Let `I_(0)` be the intensity of polarised light after passing through the first polariser P1. Then the intensity of light after passing through second polariser P2 will be
`I=I_(0)cos^(2)theta.`
Where `theta` is the angle between pass axes of `P_(1) and P_(2)`. Since `P_(1) and P_(3)` are crossed the angle between the pass axes of `P_(2) and P_(3)` will be `(pi//2-theta)`. Hence the intensity of light emerging from `P_(3)` will be
`I=I_(0)cos^(2)theta cos^(2)((pi)/(2)-theta)`
`=I_(0) cos^(2) theta sin^(2) theta =(I_(0)//4) sin ^(2)2 theta`
Therefore, the transmitted intensity will be maximum when `theta=pi//4.`