At night it is difficult to see through a closed glass window from a well-lighted room, but it is relatively easy when the room lights are switched off. Why?

On a hot summer night the refractive index of air is smallest near the ground and increases with height from the ground. When a light beam is directed horizontally the Huygen's principle leads us to conclude that as it travels the light beam

Two beams, A and B, of plane polarized light with mutually perpendicular planes of polarization are seen through a polaroid. From the position when the beam A has maximum intensity (and beam B has zero intensity), a rotation of polaroid through 30^(@) makes the two beams appear equally bright. If the initial intensities of the two beams are I_(A) and I_(B) respectively, then I_(A)// I_(B) equals:

When light travels from air to glass a change occurs in its

When light moves from glass to air, the property of it which remains unchanged is

When light enters from glass to water, which of the following quantity remains unchanged ?