what is a focal length of plane mirror

@your friends have answered this question very well. keep it up students.

In case of convex and concave mirrors (i e spherical mirrors) , the centre of curvature is the centre of the sphere of which the mirror forms a part and the radius of curvature is the radius of the sphere of which the mirror forms a part. The focal length is half of the radius of curvature. Now , let us imagine plane mirror to be a part of a sphere with infinite radius. As a result, the focal length will be infinity.


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Full define;-

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Infinity.because the distance of object from mirror"p" and the distance from image to mirror"q" are equal,so by using formula 
we can find the answer 
as the image of plane mirror is virtual,so"q" is taken negative,so putting values 
1/f=1/p-1/p(bcz p=q) 
and any thing divided by zero is infinity.

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Focal length of plane mirror is the distance between the centre of curvature and the focus.

f = dis. b/w C and F.

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Focal length of a plane mirror is infinite because we know that focal length of mirror is R/2. But the radius of curvature of plane mirror is infinte so infinit/2 is also a infinite value.

Note:- Plane mirror can be considered as concave mirror of infinte radius.

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