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in Optics by (63.5k points)

An object of size 3.0 cm is placed 14 cm in front of concave lens of focal length 21cm. Describe the image produced by the lens. What happens if the object is moved further away from the lens?

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h1 = 3 cm, u = – 14 cm, f = –21 cm. v = ?

1/v - 1/u = 1/f, 1/v = 1/u + 1/f = 1/-21 + 1/-14 = (-2 - 3)/42 = -5/42

∴ v = -42/5 = - 8.4cm So, image is errect and virtual; m = h'/h = v/u

∴ h' = v/u x h = -8.4/-14 x 3 = 1.8cm.

When the object is moved further away from the lens (u → ∞), the image moves towards the focus of lens (v → f) but never beyond f.

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