A) 1.5
B) 2
C) 1.25
D) 1.33
Correct Answer: C
Solution :
[c]: According to lens makers formula The focal length of piano convex lens is \[\frac{1}{f}=(n-1)\left( \frac{1}{\infty }-\frac{1}{-R} \right)\] \[\frac{1}{f}=\left( \frac{3}{2}-1 \right)\left( \frac{1}{R} \right)=\frac{1}{2R}\]or\[R=\frac{f}{2}\] ?.(i) The focal length of liquid lens is \[\frac{1}{{{f}_{1}}}=({{n}_{l}}-1)\left( \frac{1}{-R}-\frac{1}{\infty } \right)\] \[\frac{1}{{{f}_{l}}}=-\frac{({{n}_{l}}-1)}{R}\] \[\frac{1}{{{f}_{l}}}=-\frac{2({{n}_{l}}-1)}{f}\] (Using (i)) Effective focal length of the combination is \[\frac{1}{2f}=\frac{1}{f}+\frac{1}{{{f}_{1}}}\] \[\frac{1}{2f}=\frac{1}{f}-\frac{2({{n}_{l}}-1)}{f}\] \[{{n}_{l}}=\frac{5}{4}=1.25\]You need to login to perform this action.
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