Please solve Q 21 Q 21 Two plano-convex lenses of equal focal lengths are arranged as shown - Science - Light - Reflection and Refraction

Question

Please solve Q 21 ?
Q 21 Two plano-convex lenses of equal focal lengths are arranged as
shown

The ratio of combined focal length is
(A) 1 : 2 : 1
(B) 1 : 2 : 3
(C) 1 : 1 : 1
(D) 2 : 1 : 2

Pintu B. · Accepted Answer

Dear Student ,

In each case two plane-convex lens are placed close to each other 
So here ,1F1=1f1+1f2=1f+1f=2f⇒F1=f21F2=1f1+1f2=1f+1f=2f⇒F2=f21F3=1f1+1f2=1f+1f=2f⇒F3=f2So here the ratio of the combination of the lenses are ,F1:F2:F3=f2:f2:f2=1:1:1
Regards

Please solve Q.21 ? Q.21. Two plano-convex lenses of equal focal lengths are arranged as shown The ratio of combined focal length is (A) 1 : 2 : 1 (B) 1 : 2 : 3 (C) 1 : 1 : 1 (D) 2 : 1 : 2

Please solve Q.21 ?
Q.21. Two plano-convex lenses of equal focal lengths are arranged as shown

The ratio of combined focal length is
(A) 1 : 2 : 1
(B) 1 : 2 : 3
(C) 1 : 1 : 1
(D) 2 : 1 : 2