Alternative Energy Demystified, 2nd edition

Stan Gibilisco

Explanations for Quiz Answers in Chapter 10

1. In a long-distance transmission line, increasing the voltage (assuming a constant power demand from the set of end users) causes the current to go down in proportion. For example, doubling the voltage will reduce the current to half its former level. The power loss in the wire's resistance varies in proportion to the square of the current, so cutting the current in half will reduce the power loss to only 1/4 of its previous amount. High voltages minimize the power loss in long-distance electric transmission lines. The correct choice is C. As for choice A, higher voltages generally result in lower currents, reducing (not increasing) the magnetic field strength, so that isn't the answer. Higher voltages actually present a greater danger of electric shock than low voltages do, so B is wrong. (However, if you came into contact with a high-tension power line, the word "shock" doesn't adequately describe what would happen to you. In reality, you'd get "fried"!)

2. As described in the explanation for the answer to Question 1, doubling the voltage (assuming constant power demand from the end users) would cut the current in half, which would in turn reduce the line loss to 1/4 of its former amount. The answer is D.

3. Methane is a gas, and a methane-fired power plant is designed to burn only flammable gas. Gasoline, wood, and coal do not fall into that category, so the answer cannot be A, C, or D. As for choice B, hydrogen, some experts believe that methane-fired power plants will someday be modified to burn that gas, when and if hydrogen can be made easily available, and can be easily transported and stored. Choice B is the answer here.

4. Officials in some cities (notably Rochester, Minnesota, home of the Mayo Clinic and numerous related medical facilities) have expressed great concern about the potential for coal trains to impede ambulance services (choice C). Officials and citizens in all cities through which coal trains might pass have expressed concern over the potential for noise pollution and a decrease in the values of properties located near the tracks (choices A and B). The correct answer is D, "All of the above."

5. Before coal can be burned in a coal-fired power plant, the material must be pulverized into a fine dust. The correct choice is A.

6. A backup generator can be a great convenience on those rare occasions when the utility power fails for an extended time. However, if you don't install it properly so that it can never feed power back into the utility lines, you'll get into trouble! You must always make certain that a qualified electrician installs the proper type of isolation switch between your generator and the utility lines. The correct choice is B.

7. In a combustion-turbine type power plant that uses oil as the fuel, the generator shafts are turned by gas turbines, which resemble wind turbines that might be designed to operate in hurricanes or tornadoes. High-speed gases pass through the turbine blades, providing the torque necessary to turn the generator shafts. The correct choice is B.

8. In a conventional coal-fired power plant, the coal burns to provide heat that boils water, producing pressurized steam that drives the turbines. The correct choice is A.

9. Methane is more difficult and dangerous to transport than coal is. Methane is a gas, and as such it cause a fire or explosion if it leaks into the air. Coal won't present that sort of hazard even if it spills out in large quantities. A coal spill would simply create a huge mess. The answer is D.

10. If you're an average homeowner, your dwelling probably consumes a maximum of around 10 kW (10 kilowatts, or 10,000 watts) of power at any given time (usually much less). If you happen to live in a large home with a lot of electric appliances or with electric heating, your power demands might at times approach 20 kW. However, you'd never need more than that much power, certainly nowhere near 40 MW (40 megawatts or 40,000,000 watts as in choice A) or 60 MW (choice D). You would, however, want a generator that could provide significantly more than 500 W (choice B). A 500-W generator might power a personal computer or a few lamps and a small television set, but not more than that. The correct answer to this question is C. A 20-kW (20,000-watt) propane-fueled generator can operate almost any household for as long as the propane fuel lasts.