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Question
A divergent lens of focal length 30 cm forms the image of an object of size 6 cm on the same side as the object at a distance of 15 cm from its optical centre. Use lens formula to determine the distance of the object from the lens and the size of the image formed.
Solution
Given:
f = −20 cm (It is a diverging lens.)
v = −15 cm (Image is formed on the same side of the lens.)
Using the lens formula,
`1/f=1/v+1/u`
`->1/u=1/v+1/f`
`=1/((-15))+1/((-30))=-1/30`
∴u = 30 cm
Given: Height of the object, h = 6 cm
Height of the image, h' = ?
Magnification,` m=v/u=(h')/h`
∴ `(h')=hv/u=6xx((-15))/((-30))`
∴ h' = 3 cm
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