Convex Lens: Rays of light entering a converging lens parallel to its axis converge at its focal point F. (Ray 2 lies on the axis of the lens. ) The distance from the center of the lens to the focal point is the lens’s focal length f. An expanded view of the path taken by ray 1 shows the perpendiculars and the angles of incidence and refraction at both surfaces.

Focal .Length

10cm  

15 cm    

20 cm

30cm 

50cm

100CM

Convex             Diameter

B (i)                     50mm

B (ii)             60 mm

B (iii)              75 mm

B (iv)             100 mm