Question

24. A point light source kept at the bed of a lake of depth 10metre. The fraction of light
energy emerges from water surface is (Refractive index of water is 4/3). (Take
√7 = 2.64)​

Answer 1

3

______h

√7 is the answer

Explanation:

thank you for the question

Answer 2

Answer:

17% of light energy emerges out of the water surface.

Explanation:

Critical angle for light emerging out = $\theta = sin^{-1}(\mu_2/\mu_1)$

where, $\mu_1$ is the refractive index of air = 1

$\mu_2$ is the refractive index of water = 4/3

critical angle = $\theta = sin^{-1}(0.75)=48.59^o$

Light striking eater surface at angle more than critical anf=glr is reflected back due to Total internal reflection. Thus, a cone of light is formed below the surface of the water.

fraction of light coming out = solid angle made by conical light section / total solid angle of sphere

solid angle made by conical light section = $2\pi (1-cos(\theta))$

= $2\pi (1-cos(48.59^o))$

fraction of light coming out = $\frac{2\pi (1-cos(48.59^o))}{4\pi}$ = $\frac{(1-cos(48.59^o))}{2}$ = 0.17

It means only 17% of total light energy emerges out of the surface and rest light undergoes total internal reflection.

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