Determine the focal length of the collecting lens if the distance between the virtual image

| February 23, 2021 | education

Determine the focal length of the collecting lens if the distance between the virtual image of the object and the lens is f = 90 cm. It is known that the lens gives an increase of G = 4.0

It is known that the distance between the imaginary image of an object and the lens, according to the problem statement, is f = 90 cm = 0.9 m, and the lens gives an increase of Г = 4.0, which means that you can find the distance from the lens to this object: d = f: D or d = 0.9: 4 = 9/40 (m), since the magnification of the lens shows how many times the distance from the lens to the image is greater (less) than the distance from the lens to this object.
To determine the focal length of the collecting lens F, we use the thin lens formula: 1 / F = (1 / f) + (1 / d). Let’s substitute the values ​​of physical quantities into the formula and make calculations, taking into account that the image is imaginary (f <0), and the lens is collecting (F> 0): 1 / F = (- 1 / 0.9) + (40/9); F = 0.3 (m).



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