1)

A biconvex lens is formed with two thin plano-convex lenses as shown in the figure. The Refractive index n of the first lens is 1.5 and that of the second lens is 1.2. Both the curved surfaces are of the same radius of curvature R=74 cm. For this bi-convex lens, for an object distance of 40 cm, the image distance will be

24112021523_m9.PNG


A) -280.0cm

B) 40.0 cm

C) 21.5 cm

D) 13.3 cm

Answer:

Option B

Explanation:

 Using the lens formula

1v1u=1f=1f1+1f2

 or   1v=1u+1f1+1f2

  = 1u+(n11)(1R11R2)

 Substiuting the value , we get

 1v=140+(1.51)(1141)+

(1.21)(1114)

 Solving this equation , we get

 v=+40 cm