Two beams A and B, of plane polarized light with mutually perpendicular planes of polarization are seen through a polaroid. From the position when the beam a has maximum intensity (and beam B has zero ntensity), a rotation of polaroid through `30^circ` makes the two beams appear equally bright. If the initial intensities of the two beams are `I_A` and `I_B` respectively, then `(I_A)/(I_B)` equals:

Options

A. 3
B. `3/2`
C. 1
D. `1/3

Answer

D

Explanation

According to malus law, intensity of emerging beam is given by, `I=I_(0)cos^(2)theta`
Now, `I_(A.)=I_(A)cos^(2)30^(@)rArrI_(B.)=I_(B)cos^(2)60^(@)`
As `I_(A.)=I_(B.)rArrI_(A)xx3/4=I_(B)xx1/4rArrI_(A)/I_(B)=1/3`