A 16 cm long image of an object is formed by a convex lens on a screen placed normal to its principal axis. On moving the lens towards the screen, without changing the positions of the object and the screen, a 9 cm long image is formed again on the screen. The size of the object is:
Correct answer: C. 12 cm
- A. 9 cm
- B. 11 cm
- C. 12 cm
- D. 13 cm.
Explanation
When the lens is moved towards the screen, the height of the image formed decreases. The size of the object is determined using the displacement method, which relates the height of the object to the heights of the images formed before and after the lens is moved. In this case, the correct answer is 12 cm because the object size is the square root of the product of the heights of the images formed before and after the lens movement. Options A, B, and D are incorrect because they do not consider this relationship between image sizes and object size.
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About Optics
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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