A biconvex lens of focal length 15 cm is in front of a plane mirror. The distance between the lens and the mirror is 10 cm. A small object is kept at a distance of 30 cm from the lens. The final image is
A
Virtual and at a distance of 16cm from the mirror
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B
Real and at a distance of 16cm from the mirror
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C
Virtual and at a distance of 20cm from the mirror
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D
Real and at a distance of 20cm from the mirror
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Solution
The correct option is B Real and at a distance of 16cm from the mirror Image after refraction from lens,
1v1−1−30=115
v1=30cm
Hence the image is produced 20 cm behind the mirror.
The mirror reflects the image to produce its image at 20 cm in front of the mirror. This image acts as object for the lens.
u2=20−10=10cm
1v2−1u2=1f
Thus v2=6cm
This is the distance of image from lens.
Therefore the distance of image from mirror= 6cm+10cm=16cm