Chapter 17, Problem 98A

(a)

To determine

To prepare: A summary of different coating used in the mirrors and different advantages and disadvantages of the coating.

Explanation of Solution

Introduction:

The reflective coating in common mirrors is usually any metal deposited by a wet phase, such as silver, zinc, nickel, or chromium; or aluminum, deposited by sputtering or evaporating vacuum.

Common metal mirror coatings are formed of thin foils of aluminum, gold, or silver. Copper, beryllium, chrome, and various alloys of nickel/chrome are less common. Often with an additional dielectric layer, the metallic coating is protected (enhanced).

A significant benefit of metal-coated mirrors over dielectric mirrors is that reflectivity is very constant over a broad range, and hence, very insensitive to the incidence angle and polarization.

Drawbacks of metallic mirrors are very heavy losses found in reflection as compared to dielectric mirrors. This is obvious and the reason is that metals eventually lose some of the light of the incident.

(b)

To determine

To Prepare: A summary of the precision optical polishing of aluminum to such a degree of smoothness that no glass is needed in the process of making mirrors.

Explanation of Solution

Introduction:

In making mirrors, there should be high precision optical polishing of aluminum of such a degree of smoothness that no glass is required in this process.

With an increase in the size of the mirror made of aluminum, a deformation of an image is formed due to the mirror, and the image is mostly blurry. Thus, the aluminum mirror should be polished to a high degree of smoothness.

Conclusion:

Hence, the aluminum mirrors should be polished to a high degree of smoothness.