Question

Define magnification produced by a mirror. How is the sign of magnification related to the nature of the image.

Answer 1

Step 1:

1. Magnification is the increase in image size concerning object size.
2. It can be determined by the ratio of image size to object size.
3. Image size or height can be denoted as (h’).
4. Object size or height can be denoted as (h).
5. Magnification is otherwise called lateral magnification. It is denoted by the letter ‘M’ or ‘m’.

Step 2:

1. Signs are mainly taken as negative or positive according to sign convention.
2. Across the principal axis, the height above the principal axis is positive and the object height will always be positive because it is always kept above the principal axis.
3. But the image height can be different as it might form a virtual or real image. Height of virtual image taken as positive whereas real image height would be taken as negative.
4. Magnification can also be determined as the ratio of image distance ‘v’ to object distance ‘u' i.e. $m=-\frac{v}{u}$ : as the value of object's distance is always negative.
5. Therefore, the sign of magnification will be positive if the image is virtual and the sign will be negative if the image formed is real.