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Question
Ray optics is based on the assumption that light travels in a straight line. Diffraction effects (observed when light propagates through small apertures/slits or around small obstacles) disprove this assumption. Yet the ray optics assumption is so commonly used in understanding location and several other properties of images in optical instruments. What is the justification?
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Solution
The justification is that in ordinary optical instruments, the size of the aperture involved is much larger than the wavelength of the light used.
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