Question

An equiconvex lens is cut into two halves along (i) XOX' and (ii) YOY" as shown in fig. Let f, f', f" be the focal length of the lens, of each half in case (i), and of each half in case (ii), respectively, choose the correct statement from the following

• A. $f^{\prime }=f,f"=2f$
• B. $f^{\prime }=2f,f"=f$
• C. $f^{\prime }=f,f"=f$
• D. $f^{\prime }=2f^{\prime },f"=2f$

Answer 1

The correct option is A $f^{\prime }=f,f"=2f$

in the first case $f^{{}^{\prime }}=\frac{1}{2R}+\frac{1}{2R}=\frac{1}{R}$ i.e, $f^{{}^{\prime }}=f$

in second case $f^{\prime \prime }=\frac{1}{2R}$ i.e, $f^{\prime \prime }=2f$

option $A$ is correct