A) \[4\,f\]
B) \[2\,f\]
C) \[f\]
D) \[0.5\,\,f\,\]
Correct Answer: B
Solution :
Consider the type of lenses shown below: For bi-convex lens, focal length is given by \[\frac{1}{{{f}_{b}}}=(\mu -1)\,\,\left( \frac{1}{R}+\frac{1}{R} \right)=\frac{2(\mu -1)}{R}\] For plano-convex lens focal length is given by \[\frac{1}{{{f}_{b}}}=(\mu -1)\,\,\left( \frac{1}{R}+\frac{1}{R} \right)=\frac{(\mu -1)}{R}\] \[\Rightarrow \] \[\frac{{{f}_{b}}}{{{f}_{p}}}=\frac{\frac{R}{2(\mu -1)}}{\frac{R}{(\mu -1)}}=\frac{1=2\,{{f}_{b}}}{2}\Rightarrow {{f}_{p}}=2f\]You need to login to perform this action.
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