A concave lens of focal length \(10\) cm is cut into two identical plano-concave lenses. The focal length of each lens will be
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When a symmetrical lens is cut perpendicular to its principal axis, the power of each part becomes half.
\[
P'=\frac{P}{2}
\qquad\Rightarrow\qquad
f'=2f
\]
in magnitude.