According to Rayleigh, when sunlight travels through atmosphere, the amount of scattering is proportional to $n$th power of wavelength of light. Then, the value of 'r is

In Young' double slit experiment, if the distance between the slits is 2 mm and the distance of the screen from the slits is 100 cm , the fringe width is 0.36 mm . If the distance between the slit is decreased by 0.5 mm and the distance of the screen from the slits is increased by 50 cm , the fringe width becomes

In an experiment, two polariods are arranged such that the intensity of the polarised light emerged from the second polaroid is $37.5 \%$ of the intensity of the unpolarised light incident on the first polaroid. Then the angle between the axes of the two polaroids is

A narrow slit of width 2 mm is illuminated with a monochromatic light of wavelength 500 nm . If the distance between the slit and the screen is 1 m , then first minima are separated by a distance of