The distance between two focal points of a thin lens having focal length f is....
a. f/2
b. 2f
C. f
d. Infinity
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Explanation:
The first image will be formed from refraction from lens, its position can be determined by lens formulas
The lens formulas is given as v1−u1=f1...(i)
where u=−a,f=+f, substituting values in equation (i)
v1−−a1=f1⇒v=a−faf
The image formed will be left side of lens provide a>f
The mirror will form the image at right side of the lens with distance equal to
a−faf
Now the third image will be formed by lens again for which the coordinate system will be reversed of earlier as the rays are traveling from left to right:
u=a−faf, f=+f and v=3a
applying lens formulas
v1−u1=f1...(i)
a3−afa−f=f1...(ii) multiplying and dividing by f
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