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1)

Two beams, A and B , of plane  polarised light with mutually perpendicular planes of polarisation are seen through a polarised. From the position  when the beam  A has  maximum intensity (and beam B has  zero intensity)  , a rotation of polarised through 30° makes the two beams appear equally bright. If the initial intensities  of the  two beams are IA and IB  respectively, then IA/IB equals


A) 3

B) 3/2

C) 1

D) 1/3

Answer:

Option D

Explanation:

By law of Malus  i.e,   I=I0cos2θ

1632021117_P2.PNG

Now,   IA=IAcos2300

            IB=IBcos2600

As,           IA=IB

           IAcos2300IBcos2600

               IA34=IB14

       IAIB=13