sign convention of mirror
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Answer:
Sign is taken as + (positive) behind the spherical mirror. ...
The height of is taken as + (positive) above the principal axis and taken as – (negative) below the principal axis.
Sign Convention for Spherical Mirrors
While studying the reflection of light by spherical mirrors and the formation of images by spherical mirrors, a set of sign conventions are needed to learn that is required to measure the focal length, a distance of object or image from the mirror, and the magnification of the mirror.
Before, understanding the concept of sign conventions for spherical mirrors first discuss some commonly used terms in a spherical mirror.
Commonly used terms in Spherical mirrors
1. Aperture – The part of a spherical mirror that is exposed to all the light rays that incident on it is called the aperture of the spherical mirror. In other words, the diameter (XY) of the aperture of the concave and the convex mirror are shown in figure 1, known as its aperture.
2. Centre of curvature – The centre of a hollow sphere of which the curved or spherical mirror forms a part is called the centre of curvature. It is denoted by C (as shown in Figures 2 and 3).
3. Radius of curvature – The radius of a hollow sphere of which the spherical mirror forms a part is called the radius of curvature. It is denoted by R.
4. Pole – The centre of the spherical surface is called its pole. It is denoted by P.
5. Principal axis – The line joining the centre of curvature (C) and pole (P) of a spherical mirror and extended on either side is called the principal axis.
6. Principal focus – A point on the principal axis of a spherical mirror where the rays of light parallel to the principal axis meet or appear to meet after reflection from the spherical mirror is called the principal focus. It is denoted by F.
7. Focal plane – A plane normal or perpendicular to the principal axis and passing through the principal focus (F) of a spherical mirror is called the focal plane of the spherical mirror.
8. Focal length – The distance between the pole (P) and principal focus (F) of a spherical mirror is called the focal length of the mirror. It is denoted by f. In the figure 2 & 3 the focal length of the mirror is represented by PF.