Q102 / 160 · JIPMER 2013 · Physics

A point source of light is placed 4 m below the surface of water of refractive index $5 / 3$. The minimum diameter of a disc which should be placed over the source on the surface of water to cut-off all light coming out of water is

  • Correct answer
    A
    6 m
  • B
    3 m
  • C
    4 m
  • D
    2 m

Solution

Given, $\sin i=\frac{1}{\mu}=\frac{3}{5}$ So, $\quad \tan i=\frac{3}{4}=\frac{r}{4}$ It gives $\quad r=3 \mathrm{~m}$ So, the diameter $=6 \mathrm{~m}$.

Hence, the correct answer is option: 'A'.

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