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  4. An object is placed at a distance of 25 cm from the pole of a convex mirror and a plane mirror is set so that the virtual images formed by two mirrors do not have any parallax. The plane mirror is 20 cm from the object. The focal length of the mirror is

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Q. An object is placed at a distance of $25 \,cm$ from the pole of a convex mirror and a plane mirror is set so that the virtual images formed by two mirrors do not have any parallax. The plane mirror is $20 \,cm$ from the object. The focal length of the mirror is

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Solution:

For plane mirror, image is formed $20\, cm$ behind it as the object is $20\, cm$ in front of it. For convex mirror, Plane Mirror,
image
$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}=\frac{1}{15}+\frac{1}{-25} \Rightarrow f=37.5\, cm$