The reddish appearance of the sun of sunrise and sunset is due to :

The refractive index of glass is 1.5. The speed of light in glass is:

Two thin lenses of focal lengths f₁ = +20 cm and f₂ = -10 cm are in contact. The power of the combination is:

An unpolarized light beam travelling in air is incident on a medium of refractive index 1.73 at Brewster's angle. Then -

The intensity of transmitted light when a polaroid sheet, placed between two crossed polaroids at $22.5^{\circ}$ from the polarization axis of one of the polaroid, is ( $\mathrm{I}_0$ is the intensity of polarised light after passing through the first polaroid):

In a certain camera, a combination of four similar thin convex lenses are arranged axially in contact. Then the power of the combination and the total magnification in comparison to the power $(p)$ and magnification $(m)$ for each lens will be, respectively