A) L = 20 cm
B) L = 10 cm
C) L = 40 cm
D) L = 20 / 3 cm
Correct Answer: A
Solution :
\[\frac{1}{f}=(\mu -1)\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\] Given \[{{R}_{1}}=+\,20cm,\,{{R}_{2}}=-\,20\,cm\], \[\mu =1.5\] \[\Rightarrow \]\[f=20\]\[cm\]. Parallel rays converge at focus. So L=f.You need to login to perform this action.
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