Alternative Energy Demystified, 2nd edition

Stan Gibilisco

Explanations for Quiz Answers in Chapter 13

1. Phosphorescent materials glow when subjected to intense radiation in certain invisible forms such as high-speed electrons, UV rays, or X rays. The ionized mercury inside a mercury-vapor lamp produces great quantities of UV energy, which causes the phosphor to glow visibly white. The correct choice is B.

2. Halogen lamps can be manufactured to produce brighter light than almost any other design. (A few specialized lamps, such as carbon-arc types, can produce brighter light.) Neither a neon lamp nor an LED lamp can produce light that gets as bright as the largest halogen lamps. The correct choice is A.

3. A semiconductor type light dimmer "chops off" part of the AC waveform, so that the output voltage is effectively lower than the utility input voltage. You can control the amount of the wave that gets "chopped" using a potentiometer that controls the voltage at the gate of a silicon controlled rectifier (SCR). The answer is A.

4. Light-emitting-diode (LED) lamps don't tolerate high temperatures well. They can temporarily fail in an extremely hot room, for example, or if you enclose them in airtight chambers where the outside temperature is fairly high. (The failure isn't permanent; an overheated LED lamp will start working again after a period of cooling down.) The correct choice is C.

5. When the temperature gets low, a CFL will have trouble starting, and it will take quite awhile to reach normal brilliance if it does manage to start. In extremely cold conditions, you should not expect a CFL to work at all. The correct choice is B.

6. Of the lamp types listed here, the LED offers the best efficiency. The answer is C. That fact doesn't mean that LED lamps can produce more light than other types, however. The LED design produces more light per watt of supplied electricity than any other commonly available lamp type does, but incandescent lamps and CFLs represent better choices if you need exceptional brilliance. As previously discussed, if you need a great deal of light and electrical power consumption and efficiency don't concern you, then you're best off with a halogen lamp. Once again, the answer to this question is C.

7. The "coiled coil" geometry used in many (but not all) incandescent lamp filaments maximizes the length of wire that can fit inside the bulb envelope, helping to provide maximum energy emission in terms of the current provided. In other words, the "coiled coil" structure makes sure that the lamp has the highest practicable efficiency. The correct choice is C.

8. An LED will only glow when current flows through it in the forward direction (in other words, with forward bias). That state of affairs can exist only when the N type material is electrically negative with respect to the P type material. The correct choice is D.

9. You don't want to break any type of fluorescent lamp (including a CFL) if you can possibly avoid such an accident, because they contain a small amount of mercury, a known human toxin and environmental contaminant. The correct choice is B.

10. Inside the envelope of a conventional incandescent lamp, you'll find either a complete vacuum or an inert (nonreactive) gas at low pressure. The answer is D.