The focal length of a convex lens made of glass of refractive index (1.5) is 20 cm. What will be its new focal length when placed in a medium of refractive index 1.25 ? Is focal length positive or negative? What does it signify?

CBSE Sample Question Paper, Class 12 Physics Term 2 Question - The focal length of a convex lens made of glass of refractive index (1.5) is 20 cm. What will be its new focal length when placed in a medium of refractive index 1.25 ? Is focal length positive or negative? What does it signify?

By
Komal Kohli
-

The focal length of a convex lens made of glass of refractive index (1.5) is 20 cm. What will be its new focal length when placed in a medium of refractive index 1.25 ?
Is focal length positive or negative? What does it signify?

ANS 10 Given aஜౝ = 1.5
Focal length of the given convex lens when it is placed in air is
f = + 20 cm Refractive index of the given medium with respect to air is
aஜౣ = 1.25 New focal length of the given convex lens when placed in a
medium is f
ᇱ

New focal length is positive. The significance of the positive sign of the focal length is that given convex lens is still converging in the given medium.

RELATED ARTICLESMORE FROM AUTHOR