In mirror, magnification m = h'/h = −v/u. In lens, magnification m = h'/h = v/u. Why there is a difference in both the cases (in mirror v has negative sign while in lens v has positive sign)?
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In Negative concave and convex positive
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Magnification may be negative or positive in convex lens.
Magnification is always positive in concave lens .
Note :
- f = focal length
- v = distance of image .
- u = distance of object .
Magnification formula :
M = v / u
Concave lens :
f = negative
u = negative
v = negative
M = - v / - u = v / u
M is positive
Convex lens
f = positive
u = negative
v = positive for real image ,
v = negative for virtual image .
M may be negative or positive
The optical centre is chosen as the origin of the coordinate system.
With respect to optical centre :
The part which are above are positive, below negative.
The part which are right are positive while left is negative.
This is just like the normal x-axis and y-axis in the co-ordinate system .
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