A) \[36\sqrt{7}\]
B) \[\frac{36}{\sqrt{7}}\]
C) \[36\sqrt{5}\]
D) \[4\sqrt{5}\]
Correct Answer: B
Solution :
The radius of the light circle is given by, \[r=\frac{h}{\sqrt{{{\mu }^{2}}-1}}\] (Key concept) So, \[r=\frac{12}{\sqrt{{{\left( \frac{4}{3} \right)}^{2}}-1}}=\frac{12}{\sqrt{\frac{16}{9}-1}}\] \[=\frac{12}{\sqrt{\frac{7}{9}}}=\frac{12\times 3}{\sqrt{7}}=\frac{36}{\sqrt{7}}\]
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