Question

an object is kept at distance of 60 CM in front of convex lens real and inverted image is formed at distance of 20 cm from the lens find the focal length of lens​

Answer 1

Lens formula

1/f=1/v-1/u

1/f=1/20-(-1/60)

1/f=1/20+1/60

1/f=(3+1)/60

1/f=4/60

=1/15

There fore f= 15cm

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Answer 2

$\pmb{\bf{\underline{~ Question~:}}}$

An object is kept at distance of 60 CM in front of convex lens real and inverted image is formed at distance of 20 cm from the lens find the focal length of lens.

$\pmb{\bf{\underline{Solution~:}}}$

$Image \: formed \: \: at \: \: distance , v = 20 cm \\ \\ Distance \: of \: the \: object \: , u = 60 cm \\ \\ Focal \: length \: of \: the \: lens \: = \: ?$

$\: Using \: \: lens \: \: formula \: , \\ \\ \qquad \quad\bf{ \purple{ \frac{1}{f} = \frac {1}{v} - \frac{1}{u} }}$

$\: we \: \: get \: , \\ \\ → \: \: \: \frac{1}{f} = \frac{1}{20} - ( \frac{1}{-60}\ ) \\ \\ → \: \: \frac{1}{f} = \frac{1}{15}$

$f = 15 cm \\ \\ The \: \: focal \: \: length \: \: of \: \: the \: \: lens \: \: is \: \: \boxed{\sf\purple{15 cm}}$

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