A) 2 cm
B) 3.1 cm
C) 4.0 cm
D) 1 cm
Correct Answer: B
Solution :
\[\,\frac{{{\mu }_{r}}}{v}-\frac{{{\mu }_{i}}}{u}=\frac{{{\mu }_{r}}\,-\,\,{{\mu }_{i}}}{R}\] \[u=-\infty ;\,\,\,\,v=?;\,\,\,\,\,{{\mu }_{r}}=\,\frac{4}{3}\] \[R=+\,7.8\] \[\frac{4}{3v}\,-0\,=\,\frac{4/3-1}{7.8}\,=\,\frac{1}{3\times 7.8}\] \[v=+\,4\,\times \,7.8=31.2\text{ }mm=3.1\text{ }cm\]
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