Geometrical OpticsHard
Question
In the displacement method, a convex lens is placed in between an object and a screen. If one of the magnification is 3 and the displacement of the lens between the two positive is 24 cm, then the focal length of the lens is : -
Options
A.10 cm
B.9 cm
C.6 cm
D.16/3 cm
Solution
X = u2 - u1 = 24
m =
= 3 ⇒ v1 = 3u1 or u2 = 3u1
3u1 - u1 = 24 ⇒ u1 = 12 cm
Distance between object & screen is
D = v1 + u1 = 3u1 + u1 = 4 × 12 = 48 cm
Hence f =
=
= 9 cm
m =
= 3 ⇒ v1 = 3u1 or u2 = 3u13u1 - u1 = 24 ⇒ u1 = 12 cm
Distance between object & screen is
D = v1 + u1 = 3u1 + u1 = 4 × 12 = 48 cm
Hence f =
=
= 9 cmCreate a free account to view solution
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