Question
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
- 15 cm
- 30 cm
- 20 cm
- ¥
The correct answer is: 15 cm
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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