A screen having a real image of magnification m 1 formed by a convex lens is moved a distance x. The object is then moved until a new image of magnification m 2 is formed on the screen. The focal length of the lens is
A
B
C
D
None of these
Text Solution
Verified by ExpertsThe correct answer is:
A
In first case, 
=m 1
⇒ ⇒ 1+m 1 = 
. . . (1)
In the second case 
and 
⇒ ⇒ m 2 = 
. . . (2)
(1) and (2)
⇒ ⇒ m 2 – m 1 = x/f ⇒ ⇒ f = 
∴ ∴
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