Definition
Linear Magnification M is defined as the ratio of the image height to object height
Magnification M = (height of image)/(height of object)
Suppose an object is positioned infront of a lense as shown,
OB is the height of the object and IM is the height of the image.
If u is the object distance (PO) and v the image distance (PI), then triangle POB and PIM are similar
Hence using principles of similarities in triangles (IM/OB)=PI/PO.
Thus, image height/ object height = image distance/ object distance
Therefore Magnification,M = image distance/ object distance
I.e M = v/u
Example
An object of height 10 cm is placed 30 infront of convex lens of focal length 20 cm. Use scale drawing to find position, size and nature of the image and Magnification.
solution
we use the scale of 1cm to represent 10cm horizontally and 1cm to represent 10cm vertically. The object is represented by an upright arrow that is placed 30cm on the principal axis from the line that represents the lens.
object distance = 30cm
image distance =60cm
height of image =20cm
height of object=10cm
The image is magnified as it is bigger than the object.
The image is position at 60cm which is beyond 2F on the other side of the lens. It is a real image
Magnification M = (Image distance/object distance) = 60cm/30cm = 2
or M = image height/object height = 20cm/10cm = 2
Related Topics
- Introduction to thin lenses
- Image formation by thin lenses
- Characteristics of images formed by thin lens