Discuss with Askiitians Tutors

WHY PLANE MIRROR HAS INFINITY FOCAL LENGTH

rajan shri

14 Years agoGrade

9 Answers

PHANI TEJA

14 Years ago

plane mirror is not a sperichal mirror. hence there will be no radius and centre of curvatures. hence focal length is not defined

nikhil arora

14 Years ago

imagine any sphere whose radius is very very large (say infinity) then imagine a small part of its surface , it will be almost a plane surface (not curved) , thus a plane mirror is assumed to be a part of a spherical mirror whose radius of curvature (or focal length) is very very large (or infinite) and is said to have infinite focal length.

hope this helps !

SHUBHAM PAUL

14 Years ago

WHEN A PARALLEL BEAM OF LIGHT FALLS ON THE MIRROR ,AFTER REFLECTION THESE RAYS OF LIGHT GO IN OPPOSITE DIRECTION BY SATISFYING LAWS OF REFLECTION.THUS DUE TO THIS THEY MEET AT INFINITY WHICH IS KNOWN AS "FOCUS".THUS FOCAL LENGTH IS INFINITE.

muhammed . nabeel

14 Years ago

just experiment yourself by passing a light rays throw a plane mirror you cannot find any focal length that is because the lence is not concave or convex

pavani suhani

14 Years ago

focal length is defined to be a point at which the rays coming from an object placed at infinite distance converge. hence the focal length of a plane mirrior is infinite

B K CHAURASIYA

12 Years ago

plane mirror is a part of biggest circle whose diameter is infinity,such type of circle has infinity focal length.

Kushagra Agarwal

10 Years ago

By applying mirror formula we can find this.So apply 1/f=1/v+1/u and by keeping the values of f,v,u you will find that focal length of plane mirror is

Rishabh Shukla

9 Years ago

focal length is defined as distance btw focus and pole and focus is a point where all rays parallel to principal axis meet and in plane mirror there`s no point where rays converge it means it do not have focus and that`s why plane mirror has not focal lenth

Damini

8 Years ago

Let us consider a plane mirror to be a part of a huge sphere with a large radius of curvature(upto infinity) then if we take a small part of its surface, it turns out to be almost plane. So the radius(of the sphere of which the plane mirror forms a part) is infinity and therefore the focal length too is infinity. Mathematically,Using Mirror Formula,1/v + 1/u = 1/fWe know the image distance and object distance of a plane mirror are the same.Therefore v=uAccording to the New Cartesian Sign Convention, u is always negative. Therefore, 1/f = 1/v - 1/u => 1/f = 1/v - 1/v => 1/f = 0 => f = 1/0 = infinity