Example: 19 The power of a thin convex lens ( a μ g =1.5 ) is + 5.0 D. When it is placed in a liquid of refractive index a μ l , then it behaves as a concave lens of local length 100 cm. The refractive index of the liquid a μ l will be (a) 5 / 3 (b)4 / 3 (c) √ 3 (d) 5 / 4 Solution: (a) By using f l f a = a μ g −1 l μ g −1 ; where l μ g = μ g μ l = 1.5 μ l and f a = 1 P = 1 5 m=20 cm −100 20 = 1.5−1 1.5 μ l −1 μ l =5 / 3 Example: 9 In Young’s double-slit experiment, an interference pattern is obtained on a screen by a light of wavelength 6000 Å, coming from the coherent sources S 1 and S 2 . At certain point P on the screen third dark fringe is formed. Then the path difference S 1 P−S 2 P in microns is (a) 0.75 (b)1.5 (c) 3.0 (d) 4.5 Solution: (b) For dark fringe path difference Δ =( 2 n−1 ) λ 2 ; here n = 3 and = 6000 10 –10 m So Δ =( 2×3−1 )× 6×10 −7 2 =15×10 −7 m=1.5 microns .
Example: 19The power of a thin convex lens is + 5.0 D. When it
is placed in a liquid of refractive index then it behaves as a
concave lens of local length 100 cm. The refractive index of the
liquid will be
(a)5 / 3(b)4 / 3(c)(d)5 / 4
Solution: (a)By using ;where and
Example: 9In Youngs double-slit experiment, an interference
pattern is obtained on a screen by a light of wavelength 6000 ,
coming from the coherent sources and . At certain point P on the
screen third dark fringe is formed. Then the path difference in
microns is (a)0.75(b)1.5(c)3.0(d)4.5
Solution: (b)For dark fringe path difference here n = 3 and =
6000 1010 m
