MCQ
A lens when placed on a plane mirror then object needle and its image coincide at $15 \,cm$. The focal length of the lens is......$cm$
- ✓$15$
- B$30$
- C$20$
- D$\infty$
✓
Answer
Correct option: A.
$15$
a
(a) When the object is placed at focus the rays are parallel. The mirror placed normal sends them back. Hence image is formed at the object itself as illustrated in figure.
(a) When the object is placed at focus the rays are parallel. The mirror placed normal sends them back. Hence image is formed at the object itself as illustrated in figure.
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