Two polaroids are oriented with their planes perpendicular to incident light and transmission axis making an angle $30^{\circ}$ with each other. What fraction of incident unpolarised light is transmitted?

$$ \left(\cos 30^{\circ}=\sqrt{3} / 2\right) $$

In a single slit diffraction pattern, the distance between the plane of the slit and screen is 1.3 m . The width of the slit is 0.65 mm and the second maximum is formed at the distance of 2.6 mm from the centre of the screen. The wavelength of light used is

A ray of light from a monochromatic point source of light is incident at a point on the screen. If a thin mica film of thickness ' $t$ ' and refractive index ' $n$ ' is introduced in its path, then the optical path

Two polaroids are placed in the path of unpolarised beam of intensity ' $\mathrm{I}_0$ ' such that no light is emitted from the second polaroid. If a third polaroid whose polarisation axis makes an angle ' $\theta$ ' with the polarisation axis of first polaroid is placed between these polaroids then the intensity of light emerging from the last polaroid will be