Question

an illuminated object is placed at a distance of 30 cm in front of convex lens of focal length 20 cm the image distance is a . 60cm b. -60 cm c. 20c ​

Answer 1

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We have been given that :-

• Object distance = 30cm.
• Focal length of convex lens = 20cm
• Image distance = v = ?

Now we know according to lens formula :-

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

$\mapsto \: f = \frac{uv}{u - v}$

After inputting the known values we get :-

$\mapsto \: 20 = \frac{ - 30v}{30 + v}$

$600 + 20v = - 30v$

$600 = - 30v - 20$

$600 = - 50v$

$v = \frac{ - 600}{5 0 }$

$v = \cancel \frac{ - 600}{50}$

$v = - 12cm$

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BY SCIVIBHANSHU

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