Please help for physics question?
1 Answer
I got option (C)
Explanation:
As described in the problem the given optical system may be treated as a combination of three lenses where there are two equi-convex glass lenses of focal lengths
Now let the radius of curvature of the equi-convex lens of focal length
Similarly if the radius of curvature of the equi-convex lens of focal length
So the water lens will have two concave surfaces with radius of curvature
And the focal length of water lens
So
Now if the focal length of the combination of these three lenses be
Let us consider that the combination forms real image of twice in size of an object when object distance is
So by lens formula we have
Again if the combination forms virtual image of twice in size of an object when object distance is
So by lens formula we have
Important Note proposed by renowned and respected teacher known to us as
"Two shortcuts.
First for equi-convex lens R=f.
Second when a convex of focal length 20cm and a concave lens of focal length -20cm are placed side by side the focal length of combination is ∞. Hence, equivalent focal length of combination of three lenses reduces to the focal length of first lens."