Question

A point source is located $2.75 \,cm$ below the surface of a lake. The area of surface that transmits all the light that emerges from the surface is :

• A. $ 0.304\text{ }{{m}^{2}} $
• B. $ 30.4\text{ }{{m}^{2}} $
• C. $ 384\text{ }{{m}^{2}} $
• D. $ 3.04\text{ }{{m}^{2}} $

Answer 1

Answer: (B)

Now, using the relation
$ r=\frac{h}{\sqrt{{{\mu }^{2}}-1}} $
or $ A=\pi {{r}^{2}}=\frac{\pi {{h}^{2}}}{{{\mu }^{2}}-1} $
$ =\frac{3.14\times {{(2.75)}^{2}}}{{{\left( \frac{4}{3} \right)}^{2}}-1}=30.4{{m}^{2}} $