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

# A thin convex lens of refractive index 1.5 has 20cm focal length in air. If the lens is completely immersed in a liquid refractive index 1.6, its focal length will be :

A
160cm
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
B
100cm
No worries! Weâ€˜ve got your back. Try BYJUâ€˜S free classes today!
C
+10cm
No worries! Weâ€˜ve got your back. Try BYJUâ€˜S free classes today!
D
+100cm
No worries! Weâ€˜ve got your back. Try BYJUâ€˜S free classes today!
Open in App
Solution

## The correct option is C −160cmAccording to lens maker's formula, 1f1=[(n2−n1)n1][1R1−1R2]Here, f1 = 20 cm, n1 = 1(air) and n2 = 1.5120=[(1.5−1)1][1R1−1R2]120=(0.5)[1R1−1R2] ...............(1)Also,1f2=[(n2−n1)n1][1R1−1R2]Here, n1 = 1.6(liquid) and n2 = 1.51f2=[(1.5−1.6)1.6][1R1−1R2]1f2=(−0.0625)[1R1−1R2] ...............(2)Dividing equation (1) by (2), we getf220=0.5(−0.0625)f2=10(−0.0625)f2=−160cmHence, correct answer is option A.

Suggest Corrections
1
Join BYJU'S Learning Program
Related Videos
Thin Lenses: Point Objects
PHYSICS
Watch in App
Explore more
Join BYJU'S Learning Program