Two convex lenses of equal focal length f are placed in contact the resultant focal length of the combination is______________?
Correct answer: D. f/2
- A. zero
- B. focus
- C. 2 f
- D. f/2
Explanation
For two thin lenses in contact, their powers add: 1/F = 1/f + 1/f = 2/f. Hence F = f/2, where F and f have the same unit of length. The likely mistake is choosing c, 2f, because adding focal lengths is incorrect; it is the lens powers, or reciprocals of focal length, that add.
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Light is studied through reflection, refraction, dispersion, interference, diffraction and polarization, linking ray behavior with its wave nature. Questions may involve mirrors, lenses, optical instruments, refractive index and image formation, while geometrical optics deals with rays and wave optics explains effects such as interference and diffraction.
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