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Question
An object placed 4 cm in front of a converging lens produces a real image 12 cm from the lens.
(a) What is the magnification of the image?
(b) What is the focal length of the lens?
(c) Draw a ray diagram to show the formation of image. Mark clearly F and 2F in the diagram.
Solution
Converging lens is a convex lens.
Distance of the object from the lens (u) =-4
Distance of the image from the lens (v) = 12
(a) Magnification of the lens is given by:
`m=v/u`
⇒`m=12/-4=-3`
Thus , magnifiation produced by the llens 3.
(b) Lens formula is given by:
`1/f=1/v-1/u`
⇒`1/f=1/12-1/-4`
⇒`1/f=1/12+1/4`
⇒`1/f=(1+3)/12`
⇒`f=3`cm
(c)
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