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Question
An object is placed at a distance of 15 cm from a concave lens of focal length 30 cm. List four characteristics (nature, position, etc.) of the image formed by the lens.
Solution
Here, object distance, u = -15 cm
and focal length, f = -30 cm
Using lens formula,
`1/f = 1/v − 1/u`
`1/(−30) = 1/v − 1/(−15)`
`1/v = −1/30 − 1/15`
`v = − 10 cm`
Magnification, `m=v/u=(−10)/(−15)=+23`
Four characteristics of the image formed by the concave lens are :
(i) Image formed is virtual
(ii) Image is erect
(iii) Image is formed on the same side of the lens as the object
(iv) Image is smaller than the object
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