Answers key: Gibilisco - CHAPTER 1 MCQs

Explanations for the Answers in Chapter 1: Basic Physical Concept Quiz

• 1. An electrically neutral atom has no net electric charge, so the number of positively charged particles (protons) must equal the number of negatively charged particles (electrons). The correct answer is (c).
• 2. This question contains a distraction! The correct answer is (a). By definition, the atomic number of any atom, whether neutral or not, equals the number of protons in its nucleus.
• 3. Once again, I've inserted a distraction. The correct answer is (d). That's how we define atomic weight for any atom, electrically neutral or otherwise.
• 4. When an atom has an electric charge, we call it an ion. By definition, a positive ion is a cation. The correct answer is (b).
• 5. A carbon atom always has six protons, so we can rule out (c) and (d) straightaway. In the chapter text, we identify two different isotopes of carbon. One isotope (C12) has six neutrons, and the other (C14) has eight neutrons. The correct answer is (a).
• 6. The correct answer is (c), because we define a two-atom molecule as diatomic. Some molecules, such as O₂, have two atoms, so we can rule out (a). Molecules can have electric charge because they, like atoms, can have an excess or deficiency of electrons, so we can rule out (b). The number of protons in a molecule need not equal the number of neutrons (and often doesn't), so we can rule out (d).
• 7. A compound always contains two or more atoms. A monatomic element has single atoms (meaning that none of its atoms are bound to any other atoms) by definition, so we'll never encounter a monatomic compound. The correct answer is (a).
• 8. When a substance becomes ionized, its atoms acquire extra electrons or lose some of their electrons. The nucleus doesn't change at all. In the chapter text, we learned that ionization sometimes makes poor conductors into good conductors, so the correct answer is (a).
• 9. In the chapter text, we learned that pure elemental silver is the best known electrical conductor. The correct answer is (d).
• 10. The correct answer is (b). In the chapter text, we learned that in most gases, the atoms are too widely separated to allow for the easy passage of electrons from atom to atom. You might think that (c) is also correct, but it isn't. The electrons certainly do move in a gas! They "orbit" their "parent nuclei" at great speed (as they do in all atoms), even though they don't readily move from one atomic nucleus to another.
• 11. In the chapter text, we learned that if we impose a potential difference of 1 V across a component having a resistance of 1 ohm, we get 1 A of current. We also learned that if we double the voltage across a component whose resistance remains constant, we double the current. Therefore, the correct answer is (c).
• 12. Once again, if we double the voltage but leave the resistance unchanged, we double the current. The correct answer is (c).
• 13. We can define a hole as a place where we would normally expect to find an electron, but for some reason the electron isn't there. Holes don't have anything to do with protons, neutrons, or the existence of electron shells. The correct answer is therefore (a).
• 14. The correct answer is (a). All good conductors have low resistance. Answer (d) doesn't work, because no conductor exhibits zero resistance in the "real world." Answer (b) is absolutely wrong! You might feel the temptation to choose (c), but that statement applies to semiconductors, not to good conductors in general.
• 15. The number of electrical charge carriers on an object constitutes the quantity of its charge. We express that parameter in coulombs, so the correct answer is (d).
• 16. When a lightning stroke occurs, a potential difference is equalized by a flow of electrons from atom to atom through ionized air. The general direction of electron movement is away from the negative pole and toward the positive pole. The correct answer is (b).
• 17. The chapter text tells us that engineers express resistance in ohms. As the value in ohms increases, so does the resistance. The correct answer is (d).
• 18. A battery stores chemical energy. If we connect a component across the battery terminals so that current flows, the battery converts chemical energy to electrical energy. The correct answer is (b). Generators convert mechanical energy to electrical energy, so (a) is wrong. Motors convert electrical energy to mechanical energy, so (c) doesn't work. Obviously, answer (d) is wrong then!
• 19. A generator converts mechanical energy to electrical energy, so the correct answer is (a). Batteries convert chemical energy to electrical energy, so (b) is wrong. Motors convert electrical energy to mechanical energy, so (c) is wrong. Answer (d) is of course wrong because we've already found that answer (a) works.
• 20. No generator, battery, or motor can convert electrons into protons, so the correct answer is (d). Nobody has ever built a device that can change an electron directly into a proton.

Electronics Review Materials

Teach Yourself Electricity and Electronics, 5th edition by Stan Gibilisco

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