It is possible to distinguish between the transverse and longitudinal waves by studying the property of

Four polaroids are placed such that the optic axis of each is inclined at an angle of $30^{\circ}$ with the optic axis of the preceding one. If unpolarised light of intensity $I_0$ falls on the first polaroid,the intensity of light transmitted from the fourth polaroid is $[\cos 30^{\circ} = \sqrt{3} / 2]$.

Light waves can be polarised as they are

$A$ beam of light $AO$ is incident on a glass slab $(\mu = 1.54)$ in a direction as shown in the diagram. The reflected ray $OB$ is passed through a polaroid. On viewing through the polaroid,we find that on rotating the polaroid: (Given $\tan 57^{\circ} = 1.54$)

Consider the following statements $A$ and $B$. Identify the correct choice in the given answers.
$A$. The refractive index of the extra-ordinary ray depends on the angle of incidence in double refraction.
$B$. The vibrations of light waves acquire one-sidedness for both ordinary and extraordinary rays in double refraction.

Explain Malus's law and state its mathematical expression.