A) 3 cm
B) 9 cm
C) 12 cm
D) 24 cm
Correct Answer: B
Solution :
\[\frac{1}{f}=(\mu -1)\left[ \frac{1}{{{R}_{1}}}+\frac{1}{{{R}_{2}}} \right]\] \[\therefore \] \[f=\frac{{{R}_{1}}{{R}_{2}}}{(\mu -1)({{R}_{1}}+{{R}_{2}})}\] \[=\frac{2R\times R}{(\mu -1)\times 3R}=\frac{2R}{3(\mu -1)}\] \[\Rightarrow \] \[6=\frac{2R}{2(0.5)}\] \[\Rightarrow \] \[R=\frac{6\times 3\times (0.5)}{2}=4.5\] \[\therefore \] \[{{R}_{1}}=2R\] \[\mathbf{=9}\,\,\mathbf{cm}\]
You need to login to perform this action.
You will be redirected in
3 sec
