Question

Why are plane mirrors in reflex cameras, and the curved mirrors of telescopes, aluminized on the front surface?
A. For multiple images
B. To avoid multiple images
C. To make image fainter
D. All of the above

Answer 1

Hint: Modern mirrors are created by sputtering a thin layer of molten aluminium or silver onto the back of a glass plate in a vacuum chamber. To avoid faint reflections from the glass itself, the aluminium is evaporated onto the front surface of the glass rather than the rear in mirrors used in telescopes and other optical devices.

Complete answer:
Multiple images created by a flat mirror are typically significantly weaker than those formed by a silvered surface and go unnoticed. The extra pictures are a nuisance if silvered glass mirrors are employed in certain optical devices. Plane mirrors in reflex cameras and curved mirrors in telescopes are aluminized on the front surface for this reason. When handling these, be careful because the metallized surface is easily scratched.

Hence, the correct option is B.

Note: Multi-layer high-reflectance coatings on some mirrors can be manufactured to be more than \[99\% \] reflective for specific wavelengths of light, which is far better than silver or aluminium. These multilayer coatings are sometimes engineered to reflect one wavelength of light while allowing others to pass through. The coating may be tailored to reflect one polarisation of light while transmitting the orthogonal polarisation in some cases.Furthermore, some "mirrors" are actually prisms, with light reflecting from a face via total internal reflection, which requires no face coating.