Optics


   
 
Lens Formula
This gives the relation between focal length, object distance and image distance from the optical centre of the lens.
 
Convex Lens (Real Image)
 
 
Consider an object AB held perpendicular to the principal axis at distance beyond the focal length of the lens. A real, inverted and enlarged image is formed as shown.
 
 
 
 
 
But CD=AB
 
 
It follows
 
 
BC = -u
 
BlC = +v using sign convention
 
CF = +f
 
FBl = CBl - CF = v - f
 
 
vf = -uv + uf
 
uv = uf - vf
 
Dividing throughout by uvf
 
 
Note: (1) The above formula is applicable for a convex lens when a virtual image is formed. For this the following ray diagram is to be considered.
 
 
2) For concave lens, the ray diagram would be
 
 
Linear Magnification Produced by a Lens
 
 
Convex Lens
 
Real Image
 
 
 
 
Virtual Image
 
 
 
Concave Lens
 
 
 
 
 
     
   
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Optics