Reflection of Light Part-2
Use of Concave Mirror:
Use of Convex Mirror:
Sign Convention for Reflection by Spherical Mirrors
The conventions are as follows –
(i) The object is always placed to the left of the mirror. This implies that the light from the object falls on the mirror from the left-hand side.
(ii) All distances parallel to the principal axis are measured from the pole of the mirror.
(iii) All the distances measured to the right of the origin (along + x-axis) are taken as positive while those measured to the left of the origin (along – x-axis) are taken as negative.
(iv) Distances measured perpendicular to and above the principal axis (along + y-axis) are taken as positive.
(v) Distances measured perpendicular to and below the principal axis (along –y-axis) are taken as negative.
Mirror Formula and Magnification:
Now, that all these conventions are clear; let us know move on the mirror formula. Mirror Formula helps us to find:
- Image distance which is represented as ‘v’.
- Object distance which is represented as ‘u’.
- Focal length which is represented as ‘f’.
And is written as:
It is represented as the ratio of the height of the image to the ratio of the height of the object. Magnification is denoted as the letter ‘m’. Where,
Magnification (m) = h/h’
h’ is the image height
h is the object height
Magnification can also be related to the image distance and object distance; therefore it can also be written as:
m = -v/u
Where v is the image distance and u is the object distance.
Hence, the expression for magnification (m) becomes: