Question 170: Waves Optics

Question

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 intensity), a rotation of polaroid through $${30^ \circ }$$ makes the two beams appear equally bright. If the initial intensities of the two beams are $${{\rm I}_A}$$ and $${{\rm I}_B}$$ respectively, then $${{{{\rm I}_A}} \over {{{\rm I}_B}}}$$ equals:

Accepted Answer

According to malus law, intensity of emerging beam is given by,
$$I = {I_0}{\cos ^2}	heta $$
Now, $${I_{A'}} = {I_A}{\cos ^2}{30^ \circ }$$
$${I_{B'}} = {I_B}{\cos ^2}{60^ \circ }$$
As $${I_{A'}} = {I_{B'}}$$
$$ \Rightarrow {I_A} 	imes {3 \over 4} = {I_B} 	imes {1 \over 4}$$
$$	herefore$$ $${{{I_A}} \over {{I_B}}} = {1 \over 3}$$

Answer

$$3$$

Answer

$${3 \over 2}$$

Answer

$$1$$

Answer

$${1 \over 3}$$

Waves Optics

Choose the correct answer: