Question

A convex lens of refractive index 1.5 is dipped in turn in a liquid of refractive index

Answer 1

Focal length of lens in liquid (l)


(a) (i) ng = 1.5, nl = 1.65

ng/n1 = 1.5/1.65 < 1, so f1 and fa are  of opposite sign, so convex lens in liquid nl= 1.65 behaves as a diverging lens


so fl and fa are of same sign, so convex lens in liquid (nl = 1.33) behaves as a convergent lens

(b) (i) Focal length,



(Focal length becomes negative and its magnitude increases)

(ii) Focal length, 



 (Focal length increases)