An an image 2 by 3 of the size of the object is formed by a convex lens at the distance of 12 cm from it .find the focal length of the lens.
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An an image 2 by 3 of the size of the object is formed by a convex lens at the distance of 12 cm from it .find the focal length of the lens.
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good morning.
as per the question ,
magnification ( m ) = 2/3 , object distance ( u ) = - 12cm
now we have to take m as -ve because in convex lens the case in which the image size is less than the object then the image is also real and inverted.
m = v/u
- 2/3 = v/-12
v= 2 × 12/3
v= 8cm
now using the lens formula
1/v - 1/u = 1/f
1/8 + 1/12 = 1/f [ u = - 12 ]
taking the lcm
3 + 2 / 24 = 1/f
5/24 = 1/f
f = 24/5 cm = 4.8 cm.
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