Two converging lenses have focal length f1 and f2 . The optical axes of the two lenses coincide. This lens system is used to form an image of an object. It is observed that the size of the image does not depend on the distance between the system and object. The distance between lenses is

Question

Two converging lenses have focal length f1 and f2 . The optical axes of the two lenses coincide. This lens system is used to form an image of an object. It is observed that the size of the image does not depend on the distance between the system and object. The distance between lenses is (A) (f1 f2/f1 + f2) (B) f1+f2 (C) |f1 - f2| (D) ((f1 - f2)2/f1)

Tardigrade Admin · Accepted Answer

For 1s t lens, m1=(f1/x - f1) Where x1 is the distance of the object from 1s t lens. For 2n d lens, (Let d be the distance between the lenses) m2=(x - f1/ (d - f1 - f2) x - d f1 + f1 f2 ) Overall magnification =m1m2=(f1/ (d - f1 - f2) x - d f1 + f1 f2 ) is independent of x if d=f1+f2

$\frac{f _{1} f _{2}}{f _{1} + f _{2}}$

$f_{1} + f_{2}$

$∣ f_{1} - f_{2} ∣$

$\frac{( f _{1} - f _{2} ) ^{2}}{f _{1}}$

Q. Two converging lenses have focal length f1​ and f2​ . The optical axes of the two lenses coincide. This lens system is used to form an image of an object. It is observed that the size of the image does not depend on the distance between the system and object. The distance between lenses is

f1​+f2​f1​f2​​

f1​+f2​

∣f1​−f2​∣

f1​(f1​−f2​)2​

$\frac{f _{1} f _{2}}{f _{1} + f _{2}}$

$f_{1} + f_{2}$

$∣ f_{1} - f_{2} ∣$

$\frac{( f _{1} - f _{2} ) ^{2}}{f _{1}}$