Question

the length of a real image of an object is twice the length of the object, placed at 25cm from a convex lens. find the power of convex lens

Answer 1

Answer:

the ower of the convex lens is 2.5

Explanation:

Answer 2

The power of convex lens=6 D

Explanation:

Object distance ,u=-25 cm

Height of object =h

Height of image,h'=2h

Magnification ,m=$\frac{h'}{h}=\frac{2h}{h}=2$

$m=-\frac{v}{u}$

$2=\frac{v}{25}$

$v=2\times 25=50 cm$

Lens formula

$\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$

Substitute the values

$\frac{1}{f}=\frac{1}{50}-\frac{1}{-25}=\frac{1}{50}+\frac{1}{25}$

$\frac{1}{f}=\frac{1+2}{50}=\frac{3}{50}$

$f=\frac{50}{3} cm$

$f=\frac{50}{3\times 100}=\frac{1}{6} m$

Using 1 m=100 cm

$P=\frac{1}{f}=\frac{1}{\frac{1}{6}}=6 D$

Hence, the power of convex lens=6 D

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