Question

Define –

a. Umbra

b. Rectilinear propagation of light.

c. Point source

d. Extended source​

Answer 1

Explanation:

Umbra: An "umbra" is the part of the shadow where all of the light from the source is blocked by the shadowing object. A "penumbra" is that region around the umbra where the shadow is only partial, or imperfect. You get these when the light source is larger than a single point.

Rectilinear or propagation of light : Rectilinear propagation of light refers to the propensity of light to travel along a straight line without any interference in its trajectory

Point source: A point source is a single identifiable localised source of something. A point source has negligible extent, distinguishing it from other source geometries.For example, in astronomy, stars are routinely treated as point sources, even though they are in actuality much larger than the Earth.

Extended source : A source consisting of many point sources separated laterally and such that it has a very low degree of coherence. Thus, an extended source has a given size and subtends a given angle. See coherent sources; beam of light; diffuse light.

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