The expression for intensity (as shown in the figure) of transmitted light when a polaroid sheet is rotated between two crossed polaroids is:

[Given: I_o is the intensity of transmitted light from polariser A]

$1. \mathrm{I}=\frac{{\mathrm{I}}_0}{2}{\sin }^{2}2\mathrm{\theta }$
$2. \mathrm{I}=\frac{{\mathrm{I}}_0}{4}{\sin }^{2}2\mathrm{\theta }$
$3. \mathrm{I}=\frac{{\mathrm{I}}_0}{2}{\cos }^{2}2\mathrm{\theta }$
$4. \mathrm{I}=\frac{{\mathrm{I}}_0}{4}{\cos }^{2}2\mathrm{\theta }$

Unpolarised light is incident on a plane glass surface. What should be the angle of incidence so that the reflected and refracted rays are perpendicular to each other?

$1. {45}^0$
$2. {67}^0$
$3. {57}^0$
$4. {37}^0$