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Briefly explain Malus law about the intensity of polarised light. |
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Answer» Solution :Let intensity of plane POLARISED obtained, when UNPOLARISED light passes through a polaroid A, be `I_(0)`. Now a second polaroid B is held in the PATH of polarised light beam such that pass axis of B makes an angle `theta` from the pass axis of A as SHOWN figure (a) and (b). If amplitude of vibration of electric field vector along the pass axis of polaroid A be E, then its component passing along the pass axis of polaroid B will be `E.=Ecostheta`. `therefore` Intensity of light passed through the polaroid `I=kE^(2) and I.=kE^(.2)`, where k is a constant of proportionality. `therefore I.=kE^(.2)=k(Ecostheta)^(2)=kE^(2)cos^(2)theta=Icos^(2)theta` The relation `I.=Icos^(@)theta` is known as Malus law. (i) If `theta=0^(@)`, then `I=Icos^(2)0^(@)=I` (ii) If `theta=(pi)/(2)`, then `I.=Icos^(2)90^(@)=Ixx0=0`.  .
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