Question

what r the rules of concave and convex mirror??

Answer 1

The ray diagrams for all the six cases are as follows:

I. When the object is at infinityThe light rays coming from infinity are parallel. When parallel light rays are incident on the reflecting surface of a concave mirror, they tend to meet at its focus after reflection. In this case, the image is formed at the focus, and is point-sized.II. When the object is behind the centre of curvatureIn this case, the image is formed between the focus (F) and the centre of curvature (C). This image is real, inverted and diminished.III. When the object is at the centre of curvatureIn this case, the image is formed at the centre of curvature. This image is real, inverted and of the same size as the object.IV. When the object is between the centre of curvature (C) and the focus (F)In this case, the image is formed behind the centre of curvature. This image is real, inverted and magnified.V. When the object is at the focus (F)In this case, the image is formed at infinity. This image is real, inverted and highly enlarged.VI. When the object is placed between the focus (F) and the pole (P)In this case, the image is formed behind the mirror. This image is virtual, erect and magnified.

The discussion is summarised in the table given below.

Object positionImage positionSize of imageNature of imageAt infinityAt FPoint-sizedRealBeyond CBetween F and CSmallReal and invertedAt CAt CSame as that of the objectReal and invertedBetween C and FBehind CEnlargedReal and invertedAt FAt infinityHighly enlargedReal and invertedBetween F and PBehind the mirrorEnlargedVirtual and erect
Images Formed by Convex Mirrors

A convex mirror always produces virtual and erect images of very small size. The images formed by a convex mirror are primarily classified in two ways.

I. When the object is at infinity

In this case, the image appears to form at the focus. This image is virtual, erect and very small in size.


 

II. When the object is between the pole (P) and a point X (X lies beyond C)

In this case, the image is formed between the pole (P) and the focus (F), behind the mirror. This image is virtual, erect and small in size.

 

These results are summarised in the following table.

Object positionImage positionSize of imageNature of imageAt infinityAt FExtremely smallVirtual and erectBetween P and X (X lies beyond C)Between P and FSmallVirtual and erect

Answer 2

and the first rule for concave mirror and convex mirror is that if a rayis parallel to the principal axis, then it will pass through the focus of the mirror.