Question

Explain the difference:
a) Point sources and extended sources of light.
b) Umbra and penumbra.

Answer 1

Ans a) Point source is particularly localised emission or source of light at a point which decreases in proportiom to the inverse square of distance from the source while extended source are collection of such point sources of light together.
Ans b)The umbra is the center part or the darkest part of the shadow. The penumbra is an extended part of the shadow that is slightly lighter than the umbra where some or all of the light sources are obscured.

Answer 2

1. a)point source of light

i) any source of light that has a negligible extent.

ii) shadows are uniformly dark, sharp at the edges and bigger than the objects .

iii) example-stars at distant , astronomy ,etc.

b) extended source of light

i) a source containing of many point sources separated laterally.

ii) two types of shadows are formed-1. when source of light is one smaller than the object and number. 2.once bigger than the object.

iii) examples-fluorescent bulbs, sun,etc.

2. a) Umbra

i) during the formation of shadow the central dark region is called Umbra.

ii) no Ray of light enters into this region.

b) Penumbra

i) during the formation of shadow the outer less darker region is called penumbra .

ii) it receives a few light of rays only and so is less darker.

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