Question

an object is placed at a distance of 75 cm from a screen where should a convex lens of focal length 12 CM can be placed so as to obtain four times magnified real image of the object on the screen

1. 20 cm from object
2. 40 cm from object
3. 24 cm from object
4. 15 cm from object

please guys please guys answer the question with the full step is with explanation I will mark it as brain list answer.

Answer 1

The object can be placed at 15 cm.

Explanation:

D=75 cm,f=12 cm  

D>4 f, there will be two positions of lens for which real image can be

obtained

for lens in position.

Given data:

u = −x

v = D−x=75−x

f = 12 cm

1/v−1/u=1/f

1 / 75−x − 1/−x = 1/12

75 / (75−x)x = 1/12

x^2 −75 x + 900 = 0

(x−15) (x−60) = 0

x = 15  or 60 cm

The object can be placed at 15 cm

Also learn more

A concave lens forms the image of an object such that the distance between the object and the image is 10 centimetre and magnification produced is 1 / 4 find the focal length of the lens?

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