Teach Yourself Electricity and Electronics, 5th edition
Stan Gibilisco
Explanations for Quiz Answers in Chapter 7
1. In a stand-alone solar power system, the electric utility company plays no role. The correct answer is (c). Choice (a) is totally wrong; the truth is precisely the opposite. The batteries drive the system at night, and the batteries recharge when the sun shines on the solar panels. Choice (b) is inaccurate; a good stand-alone solar power system can operate all kinds of appliances, even sophisticated electronic devices. Choice (d) is wrong as well; it describes one of the benefits of an interactive, but not a stand-alone, solar power system.
2. A battery discharge graph typically portrays the output current (in amperes on the vertical axis) as a function of time (in hours on the horizontal axis). The area of the region bounded by the discharge curve (on top), the current axis (on the left) and the time axis (on the bottom) gives us an indication of the total battery capacity in ampere-hours. Choice (a) is correct. The other choices are all irrelevant because none of them take time into consideration.
3. Primary cells don't allow for recharging. Once we use a primary cell up, it's done for, and must be discarded. If we connect several primary cells in series, therefore, we obtain a primary battery that that can't be recharged and should be thrown away when it "dies." The right answer is (d). Choice (a) is absolutely wrong; it describes a secondary battery made from secondary cells. Choice (b) might work for a primary battery made from cells having a certain chemical composition, but not for primary batteries in general (the question says "any battery"). Choice (c) is entirely irrelevant; in fact, no known component produces AC directly from visible light.
4. You must pay close attention to the wording of this question, or it might fool you. The output voltage of an electrochemical cell under no-load conditions (when it doesn't have to supply any current) depends on the chemical composition, but not on the mass or volume. For example, a size AA zinc-carbon cell produces the same no-load voltage as a size D zinc-carbon cell, even though the D cell has several times the mass and volume of the AA cell. The correct answer is (c).
5. When we connect two or more identical electrochemical cells in parallel, the no-load voltage across the combination remains the same as it would be across a single cell. No matter how many cells we connect in parallel, the no-load voltage never changes if all the cells are identical. The correct answer is (b).
6. This question will mislead you if you don't read it carefully. Under no-load conditions, by definition, an electrochemical cell (or a power supply of any kind, for that matter) is not called upon to deliver any current whatsoever. The correct answer is therefore (d).
7. A power inverter converts DC, usually at a low or moderate voltage, into AC suitable for operating conventional household appliances. The correct answer is (b). The other choices are all clearly wrong.
8. Memory drain is a phenomenon peculiar to nickel-based rechargeable cells and batteries, particularly the nickel-cadmium (NICAD) type. The cell or battery holds less charge than it should. It doesn't work for very long before it "runs out of juice." Other rechargeable cells, such as the lithium type, do not exhibit memory drain. The correct answer is (c).
9. When we connect two or more identical electrochemical cells in series, their no-load voltages add up, but the maximum deliverable current does not change. If we connect five cells in series, each of which provides 1.5 V DC under no load, the battery will give us 1.5 x 5, or 7.5 V DC in the absence of a load. However, the battery will only be capable of delivering 12 A, just as a single cell would do. The correct answer is (c).
10. By definition, a secondary cell can be recharged after its chemical energy has all gone into electrical energy. The correct answer is (c). Choice (a) is wrong; chemical energy represents a form of potential energy, but not kinetic energy. Choice (b) describes a primary cell or battery, not a secondary device. Choice (d) describes a photovoltaic cell or battery.
11. We can use Ohm's Law to calculate how much current the 600-ohm resistor draws from a battery that supplies 6.00 V DC. Dividing the voltage by the resistance, we get 0.0100 A. We've been told that the battery has a capacity of 4.80 Ah. If we leave the resistor connected continuously for 480 h (20 full days), we'll have used up all the available energy in the battery because

0.0100 A x 480 h = 4.80 Ah

The correct answer is (d), assuming that the battery has a flat discharge curve, so that the current drops to zero instantly when the battery has lost all of its charge. (No "real-world" battery exhibits such a perfect discharge characteristic.)
12. By definition, a standard cell having a particular chemical composition always produces a predictable, precise no-load output voltage. The correct answer is (a).
13. A wall clock with a liquid crystal display (LCD) consumes very little power in operation. In fact, it draws so little current that a single, small electrochemical cell can power it for months. The correct answer is (a). Although a lantern battery (b) will power an LCD wall clock, that type of battery would add a lot of unnecessary bulk and mass to the clock. The same holds true for (c); a fuel cell would not only be big and heavy, but would cost a lot! Choice (d) is interesting; if an LCD clock were placed in a location such that visible light always shone on it, a small photovoltaic cell or panel would power it. However, you will not likely see an LCD clock powered that way, because constantly illuminated locations are rare.
14. A zinc-carbon cell delivers approximately 1.5 V DC output under no-load conditions, regardless of its physical size or mass. Therefore, choice (a) cannot work; nothing can "depend" on a constant! The physical length alone doesn't directly affect the energy that a zinc-carbon cell can provide over time (a cell can be long and thin or short and fat), so (b) is not strictly true. However, the physical volume does indeed affect the total energy available from the cell. The correct answer is (c). Answer (d) will not work at all. All zinc-carbon cells exhibit the same electrode polarity behavior.
15. If a battery's maximum deliverable current diminishes steadily over time while in continuous use, we say that the battery exhibits a declining discharge curve. The correct answer is therefore (b).
16. A fuel cell of the proton exchange membrane (PEM) type produces approximately 0.7 V DC under no-load conditions. When we connect two or more identical cells of any type in series, their individual voltages add up. Therefore, four identical PEM fuel cells in series gives us a stack having a no-load output voltage of 0.7 x 4, or 2.8 V DC. The correct answer is (d).
17. Button cells have small volume, and therefore small energy capacity and limited maximum deliverable current. Such a cell will run a wristwatch, but would be far too small to function effectively in a stand-alone solar power system or as the main power source for a portable amateur radio transmitter. The correct answer is (a).
18. The cadmium in any nickel-cadmium (NICAD) cell or battery constitutes an environmental pollutant and a biological toxin. Nickel-metal-hydride (NiMH) cells and batteries do not contain cadmium or any other highly dangerous substance. Choice (a) is therefore the best answer here. Choice (b) is wrong because NICAD cells and batteries exhibit memory drain, and it's a nuisance, not a benefit. Choice (c) is wrong because both NiMH and NICAD devices can hold a charge from solar panels. Choice (d) is wrong because both NiMH and NICAD cells will work okay in series combinations.
19. We can connect solar cells in series to get more voltage than a single cell provides, so choice (a) will work. We can connect four cells in a 2 x 2 series-parallel matrix, getting twice the voltage that a single cell alone would provide, so (b) will also work. Choice (c) is wrong because connecting multiple cells in parallel won't increase the voltage over that of a single cell. Because both (a) and (b) constitute plausible answers to this question, the correct choice is (d), "More than one of the above."
20. Solar cells are extensively used in spacecraft, but they rarely constitute an important energy source for flashlights, lanterns, portable amateur radio transmitters, or cellular telephone sets. Therefore, the correct answer is (b).