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The focal length of convex lens is 30 cm...

The focal length of convex lens is 30 cm and the size of image is quarter of the object, then the object distance is

A

90 cm

B

60 cm

C

30 cm

D

50 cm

Text Solution

Verified by Experts

The correct Answer is:
A
`f=30cm, v=(u)/(4)`
For a convex lens, v is +ve, f is +ve
and `(1)/(f)=(1)/(v)-(1)/(u) therefore (1)/(u)=(1)/(v)-(1)/(f)`
`therefore (1)/(u)=(1)/(u//4)-(1)/(30)=(4)/(u)-(1)/(30)`
`therefore (1)/(u)-(4)/(u) = -(10)/(30) therefore -(3)/(u)= -(1)/(30)`
`therefore u=90 cm`
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