| Alternative Energy Demystified, 2nd edition |
| Stan Gibilisco |
| Explanations for Quiz Answers in Chapter 12 |
| 1. If we have a five-by-five array of identical solar cells (for a total of 25 cells), each one of which can provide up to 0.40 watts of power, then the entire array can theoretically provide us with up to 25 x 0.40 = 10 watts of power. When we combine identical solar cells in any series, parallel, or series-parallel array, the total amount of power available from the whole set equals the power available from any single cell, times the total number of cells in the set. The correct choice is D. |
| 2. The Einstein equation tells us that the energy contained in a given amount of matter varies directly in proportion to its mass. Therefore, if we double the mass of a sample (as this question implies), we double the amount of energy that we could get from it, if we could develop some way to actually convert all the mass in a sample directly into energy. The correct choice is B. |
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3. This question describes a six-by-six series-parallel array of identical solar cells, each of which can produce up to 1.5 amperes of current. The array might have either of the following geometries:
In the first case, each set of six series-connected cells can produce 1.5 amperes (currents do not add in series, but stay the same; in fact, we have only one current in a series circuit, and it's the same at every point in that circuit). When we connect six such sets in parallel, we get 6.0 x 1.5 = 9.0 amperes as the maximum current to expect (currents add arithmetically in parallel). In the second situation, each set of parallel-connected cells can produce up to 1.5 x 6.0 = 9.0 amperes (once again, currents in parallel add up). When we connect six such sets in series, we get the same 9.0 amperes (once again, currents in series stay the same). Either way, we get 9.0 amperes as the maximum current to expect from the array. The answer is B. |
4.The situation here is "inside-out" from the one
in Question 3. Once again, we have a six-by-six series-parallel array
of identical solar cells, each of which can produce up to 0.5
volt. As before, our array can have either of the following
geometries:
In the first case, each set of six series-connected cells can produce 0.5 x 6.0 = 3.0 volts (voltages add up in series). When we connect six such sets in parallel, we still have a maximum of 3.0 volts (identical voltages in parallel do not add up; we get the same voltage as we would get from any one of the components all by itself). In the second situation, each set of parallel-connected cells can produce only a maximum of 0.5 volts (once again, voltages in parallel do not add). When we connect six such sets in series, we get 0.5 x 6.0 = 3.0 volts (as before, voltages in series do add up). Either way, we can expect to get up to 3.0 volts from the complete matrix. The correct choice is D. |
| 5. The conversion efficiency of a photovoltaic (PV) cell equals the ratio of the available electrical output power to the total visible-light power striking the cell, assuming we use the same units (such as watts) to express both quantities. The correct choice is D. |
| 6. When scientists talk about atomic nuclei, they use the term "unstable" to mean that the nuclei tend to decay as time goes by. Atomic nuclei generally do not accumulate neutrons, so choice A is wrong. Although nuclei can, in some sense, grow more massive (as happens in hydrogen fusion, for example), we don't refer to those nuclei as "unstable," so choice B is wrong. Atomic nuclei don't contain electrons at all, so they never gain or lose them; choice D is completely off the mark! We're left only with choice C, and that's the right answer here. Scientists call nuclei that decay over time "unstable." |
| 7. The angle q, as shown in the geometry of Fig. 12-13, should equal 90 degrees minus the latitude of the location where the solar panel will be installed. The latitude at Fairbanks, Alaska is 65 degrees north (to the nearest degree). Therefore, you should set the angle q to 90 - 65 = 25 degrees. The correct choice is A. |
| 8. By definition, the four phases of matter are solid, liquid, gas, and plasma. The correct choice is C. |
| 9. Electrons carry negative electrical charge. If an atom loses one or more electrons, then its electrical charge becomes less negative, which means the same thing as more positive. The answer is A. |
| 10. All three of the choices A, B, and C state advantages of an interactive small-scale PV system without batteries. Therefore, the answer is D, "All of the above." |