Two polaroids $P_1$ and $P_2$ are placed with their axes perpendicular to each other. Unpolarised light of intensity $I_0$ is incident on $P_1$. $A$ third polaroid $P_3$ is kept in between $P_1$ and $P_2$ such that its axis makes an angle $45^{\circ}$ with that of $P_1$. The intensity of transmitted light through $P_2$ is

Three polaroid sheets are co-axially placed as indicated in the diagram. Pass axes of the polaroids $2$ and $3$ make $30^{\circ}$ and $90^{\circ}$ with the pass axis of polaroid sheet $1$. If $I_0$ is the intensity of the incident unpolarised light entering sheet $1$,the intensity of the emergent light through sheet $3$ is

Which of the following is a biaxial crystal?

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.

For light of intensity $I_0$,a polaroid is placed at an angle of $45^\circ$. What will be the intensity of the light passing through the polaroid after polarization?

Three linear polarisers are placed coaxially. The transmission axis of the first polariser is at $30^{\circ}$,the second one is at $60^{\circ}$,and the third at $90^{\circ}$ to the vertical,all in the clockwise sense. Each polariser additionally absorbs $10 \%$ of the light. If a vertically polarised beam of light of intensity $I=100 \, W/m^2$ is incident on this assembly of polarisers,then the final intensity of the transmitted light will be close to ................ $W/m^2$.