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Question
An object is placed at a distance of 4 cm from a concave lens of focal length 12 cm. Fine the position and nature of the image.
Solution
Object distance u = -4 cm (left side of the lens)
Focal length f = -12 cm (left side of the lens)
Image distance v = ?
From the lens formula, we know that:
`1/v-1/u=1/f`
Substituting the values of v and u, we get:
`1/v-1/u=1/f`
⇒`1/v-1/-4=1/-12`
⇒`1/v=-1/12-1/4`
⇒`1/v=(-3-1)/12`
⇒`1/v=(-4)/12`
⇒`v=12/-4`
⇒`v=-3` cm
Thus, the image is virtual and formed 3 cm away from the lens, on the left side.
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