1
You visited us 1 times! Enjoying our articles? Unlock Full Access!
Question

# A biconvex lens has a focal length of 10 cm. It is cut in half and two pieces are placed as shown. The focal length of the final combination in cm is

A
10
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
B
20
No worries! We‘ve got your back. Try BYJU‘S free classes today!
C
40
No worries! We‘ve got your back. Try BYJU‘S free classes today!
D
Not a lens
No worries! We‘ve got your back. Try BYJU‘S free classes today!
Open in App
Solution

## The correct option is A 10Before breaking the focal length of the lens can be found out as shown below 1f=(μ−1)(1R1−1R2)=(μ−1)[1R1−(−1R2)] 1f=(μ−1)2R⇒f=R2(μ−1) After breaking, let the focal length of the leftmost lens be f1 1f1=(μ−1)(1∞−(−1R)) 1f1=(μ−1)(1R) f1=R(μ−1) f1=2f=20 cm let the focal length of the rightmost lens be f2 1f2=(μ−1)(1R−1∞) 1f2=(μ−1)(1R) f2=R(μ−1) f2=2f=20 cm 1fnet=1f1+1f2 120+120=110 fnet=10 cm

Suggest Corrections
7
Join BYJU'S Learning Program
Related Videos
Combination of Lenses and Mirrors
PHYSICS
Watch in App
Join BYJU'S Learning Program