Three identical polaroids $P_1$, $P_2$ and $P_3$ are placed one after another. The pass axis of $P_2$ and $P_3$ are inclined at angle of $60^\circ$ and $90^\circ$ with respect to axis of $P_1$. The source has an intensity $I_0$. The intensity of light finally coming out is

In Young's double slit experiment, two slits are illuminated with a light of wavelength $\lambda$. The line joining $A_1P$ is perpendicular to $A_1A_2$ as shown in figure. If the first minimum is detected at P, the value of slits separation 'a' will be
(D = distance between source and screen)

In Young's double slit experiment, the fringe width is 0.4 mm. What is the distance between $4^{\text{th}}$ dark band and $6^{\text{th}}$ bright band on the same side of the interference pattern?

The ratio of intensities at two points on the screen in Young's double slit experiment when waves from the two slits have a path difference of zero and $\lambda/4$ is ($\lambda$ is the wavelength of light used) ($\cos 0^\circ = 1$, $\cos\pi/2 = 0$)