In an experiment, an object was placed on the principal axis of a convex lens 25 centimeters away from the lens. A real image 4 times the size of the object was obtained. The focal length of the lens is:
Correct answer: A. 20 cm
- A. 20 cm
- B. 25 cm
- C. 33 cm
- D. 50 cm
- E. 100 cm
Explanation
The explanation is given below:u = 25 cmm = -4 [a real image so it must be inverted]v = - m * u = - * (-4) * 25 = 100 cmf = u * v / (u + v) = 25 * 100 / (25 + 100) = 2500 / 125 = 20 cmSo the focal length of the lens is 20 cm.
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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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