What is a polarizer and an analyser?

When an unpolarized light of intensity $I_o$ is incident on a polarizing sheet,the intensity of the light which does not get transmitted is

An unpolarized light passes through three polarizing sheets whose polarizing directions make an angle of $30^o$,$60^o$,and $30^o$ with the $y$-axis in the same sense. What fraction of the initial intensity is transmitted by the system?

An unpolarised light beam of intensity $2 I_{0}$ is passed through a polaroid $P$ and then through another polaroid $Q$ which is oriented in such a way that its passing axis makes an angle of $30^{\circ}$ relative to that of $P$. The intensity of the emergent light is.

$A$ point source $S$ emits unpolarized light uniformly in all directions. At two points $A$ and $B$,the ratio $r = I_A / I_B$ of the intensities of light is $2$. If a set of two polaroids having $45^{\circ}$ angle between their pass-axes is placed just before point $B$,then the new value of $r$ will be.

An unpolarized light beam of intensity $I_0$ is incident on a polarizer $A$ and then passed through a second polarizer $B$. If the principal plane of polarizer $B$ makes an angle of $45^\circ$ with respect to polarizer $A$,the intensity of the emerging light will be ........