A) Air and placed in air
B) Air and immersed in L1
C) L1 and immersed in L2
D) L2 and immersed in L1
Correct Answer: D
Solution :
\[\frac{1}{f}=\left( \frac{{{n}_{2}}}{{{n}_{1}}}-1 \right)\,\,\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\] where \[{{n}_{2}}\] and \[{{n}_{1}}\] are the refractive indices of the material of the lens and of the surroundings respectively. For a double concave lens, \[\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\] is always negative. Hence \[f\] is negative only when \[{{n}_{2}}>{{n}_{1}}\]You need to login to perform this action.
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