With a neat labelled diagram, explain the terms total internal reflect

1.	With a neat labelled diagram, explain the terms total internal reflection and critical angle.
Answer» Solution :Passage of light from water ( DENSER medium ) to air ( rarer medium ) . The ray of light incident at the BOUNDARY separating the two media bends away from the normal on refraction. Here, the angle of refraction `r, ` is greater than the angle of incidence i. Now `._(a)n_(w ) = ( sin i)/(sin r )LT 1 `. Here,` ._(a)n_(w )` is the refractive INDEX of air with respectto water. As `._(a) n_(w)` is constant, r increases as i increases. For `r= 90^(@)`, the ray travels along the boundary. If i is increased further, as r cannot be greater than `90^(@)`, light does not enter air. There is no refraction of light and all the light enters water on reflection. This is called total internal reflection. For `r = 90^(@) , ._(a) n_(w) = ( sin i )?( sin 90^(@))= sin i `. This angle i is called the critical angle.

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