A) convex mirror of focal length\[10cm\]
B) concave mirror of focal length\[40cm\]
C) concave mirror of focal length\[60cm\]
D)
concave mirror of focal length
Correct Answer: A
Solution :
When two lenses are kept in contact, the combined focal length of the combination is \[\frac{1}{F}=\frac{2}{f}+\frac{1}{{{F}_{m}}}\] For a plane mirror,\[{{f}_{m}}=\infty \] \[\therefore \] \[F=\frac{f}{2}=\frac{20}{2}=10\,\,cm\] Hence, arrangement behaves as a convex mirror of focal length\[10cm\].
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