An object of 5 cm is kept at a distance of 25 cm from concave lens of focal length 10 cm. Calculate the distance of the image from the lens and size of the image.

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Solution

Given : $u = - 25 c m$ $f = - 10 c m$ $h_{o} = 5 c m$
Using $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$
Or $\frac{1}{v} - \frac{1}{(- 25)} = \frac{1}{(- 10)}$
$⟹ v = - 7.14 c m$
Height of image $\frac{h_{i}}{h_{o}} = \frac{v}{u}$
Or $\frac{h_{i}}{5} = \frac{- 7.14}{- 25}$
$⟹ h_{i} = 1.43$

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An object of 5 cm is kept at a distance of 25 cm from concave lens of focal length 10 cm. Calculate the distance of the image from the lens and size of the image.

Given : u=−25 cm f=−10 cm ho=5 cmUsing 1v−1u=1fOr 1v−1(−25)=1(−10)⟹ v=−7.14 cmHeight of image hiho=vuOr hi5=−7.14−25⟹ hi=1.43

Given : $u = - 25 c m$ $f = - 10 c m$ $h_{o} = 5 c m$
Using $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$
Or $\frac{1}{v} - \frac{1}{(- 25)} = \frac{1}{(- 10)}$
$⟹ v = - 7.14 c m$
Height of image $\frac{h_{i}}{h_{o}} = \frac{v}{u}$
Or $\frac{h_{i}}{5} = \frac{- 7.14}{- 25}$
$⟹ h_{i} = 1.43$