If an object is placed $25 c m$ in front of the converging lens forms an image $20 c m$ behind the lens, then what is the focal length of the lens ?

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Solution

$u = - 25 c m v = 20 c m$
lens formula
$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
$\frac{1}{f} = \frac{1}{20} - (\frac{1}{- 25})$
$f = 11.11 c m$
focal length of the lens = $11.11 c m$

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If an object is placed 25cm in front of the converging lens forms an image 20cm behind the lens, then what is the focal length of the lens ?

u=−25cmv=20cmlens formula 1f=1v−1u1f=120−(1−25)f=11.11cmfocal length of the lens = 11.11cm

If an object is placed $25 c m$ in front of the converging lens forms an image $20 c m$ behind the lens, then what is the focal length of the lens ?

$u = - 25 c m v = 20 c m$
lens formula
$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
$\frac{1}{f} = \frac{1}{20} - (\frac{1}{- 25})$
$f = 11.11 c m$
focal length of the lens = $11.11 c m$