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A mirror is polished with coarse sandpaper instead of a fine one. Using the law of reflection, what happens to the image it forms?
AThe surface starts transmitting rather than reflecting light
BThe image is unaffected, since reflection ignores surface texture
CThe surface becomes smoother, sharpening the image
DThe surface becomes irregular, blurring the image
Answer & Solution
Correct answer: D. The surface becomes irregular, blurring the image
1. The law of reflection sends each ray off at an angle equal to its angle of incidence, measured from the local surface normal.
2. Coarse sandpaper roughens the mirror, so different tiny patches of the surface face slightly different directions.
3. Parallel incoming rays then leave at many different angles rather than one, which is exactly what diffuses and blurs an image.
4. A smoother surface would sharpen the image instead, so coarse sandpaper achieves the opposite of a fine polish.
_Source: OpenStax Physics (CC BY 4.0), Ch 16 "Mirrors and Lenses", section 16.1 Reflection_
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