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4. Intensity Of Light
W ith regards to light as generally believed by all scientists, we also accept that the intensity of light depends upon the number of photons.
Intensity of any kind of radiation depends upon the number of incident particles i.e. photons per unit area per unit time. As the distance between the source of light and light receiving surface increases, intensity decreases with a proportion to be reciprocal of the distance square because the number of photons received by that surface decreases. It is denoted as follows.
Ta 1/d2 (Where I is intensity and 'd' is distance between source of light and light receiving surface}
::1 = k/d? (Where K is constant for the same source of light and it denotes total number of photons per unit time emitted by a source and it depends upon emissive power of the metal}.
- 1= x 2 (K=n/t, n depends upon emissive power and light-velocity
n=egc)
I=S
.
(Where e depends upon an area of emitting surface, o =
t.do
Nandighosh constant and its unit may be joule.sec/meter. c = velocity of light. d = distance between the source of light and light receiving surface)
But photons are scattered in all directions, the number of photons per unit area decreases with proportion to 1/4 nr?: Here r = d.
:.1= OCOR e or
4 atd
4
trz
If either a source of light or a light receiving surface is in motion and they come nearer to each other, their velocity becomes negative then = d-v.t, where d is an initial distance between the source of light and light
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