Electronics Demystified, 2nd edition Stan Gibilisco Explanations for Quiz Answers in Chapter 11 1. The octal numeration system has eight single digits: 0, 1, 2, 3, 4, 5, 6, and 7. The digit sequence 999 has no meaning in the octal system. The correct choice is D. 2. The megabyte (MB) is a unit of digital data storage, equivalent to 220 or 1,048,576 bytes. One byte represents eight bits of data, so in theory, 1 MB contains 1,048,576 x 8 = 8,388,608 bits. The megabit per second (Mbps) is a unit of digital data speed representing 106 or 1,000,000 bits per second (bps). The correct choice is A. We use the megabyte to quantify stored data. We use the megabit per second to quantify data transfer speed. 3. Biometric security technology involves measuring or scrutinizing some characteristic of a person's body to verify identity. Such characteristics include fingerprints, thumbprints, handprints, iris patterns, voice patterns, or facial features. Usernames, identification numbers, and passwords do not constitute biological parameters. The correct answer is B. 4. Once in awhile, you'll hear or read about baud, bauds, or baud rate in regards to digital data speed. In theory, one baud equals one change of state (high-to-low or low-to-high) per second. The number of bauds equals the number of times per second that the data state changes. The correct choice is B. Choice A is not right. Kilobits, in theory, can quantify stored data, although you'll rarely hear or read about kilobits all by themselves; you'll more likely encounter kilobits per second (kbps) representing data transfer speed. Megabytes quantify stored data, so choice C is wrong. The term kilobyte-second has no meaning in terms of data storage, transfer rate or transition rate, so choice D is irrelevant. 5. A low-earth-orbit (LEO) network employs satellites whose orbits are much closer to the earth's surface than the orbit of any geostationary satellite. Therefore, it takes less time for wireless signals to reach and return from a LEO satellite (or even to pass through a "chain" of two or more LEO satellites) as compared with a geostationary satellite. In practical terms, the shorter propagation-path length translates to reduced latency with the LEO system. The correct choice is A. The altitude of a communications satellite has nothing to do with its reliability or its ability to handle high-speed data, so choices B and C are wrong. 6. The circuit described here receives serial data and converts it to parallel data. It's a serial-to-parallel (S/P) converter. The correct choice is C. 7. The correct choice is D. The military uses the most sophisticated available encryption methods in sensitive wireless communications. Amateur radio communications offer no security whatsoever; anyone with a good all-wave radio receiver can eavesdrop, so choice A is wrong. Most commercial wireless and cellular telephone systems offer some security and privacy, but far less than that of a typical secret military communication, so choices B and C are wrong. 8. The decimal numeral 64 represents the same quantity as the octal numeral 100. To see why, we recall that the rightmost digit in an octal numeral quantifies the "ones"; the second digit from the right quantifies the "eights"; the third digit from the right quantifies the "64s". Therefore, the octal numeral 100 represents (0 x 1) + (0 x 8) + (1 x 64) = 64 in decimal terms. The correct choice is D. 9. In an e-mail address, the character sequence following the last dot (which looks like a period or decimal point) tells us the type of domain that the network employs. The correct choice is C. 10. The answer is D. The decimal numeral 129 represents the same quantity as the binary numeral 10000001. To see why, let's remember how we construct binary numerals. The choices in this question contain up to eight binary digits (but never more than that, thankfully!). Starting at the extreme right, an eight-digit binary numeral breaks down as follows: The rightmost digit represents units of 20 or 1 The second digit from the right represents units of 21 or 2 The third digit from the right represents units of 22 or 4 The fourth digit from the right represents units of 23 or 8 The fifth digit from the right represents units of 24 or 16 The sixth digit from the right represents units of 25 or 32 The seventh digit from the right represents units of 26 or 64 The eighth digit from the right represents units of 27 or 128 If we scrutinize each of the numerals given here, we'll find that choice D gives us the correct answer. In the numeral 10000001, the rightmost digit adds 1 to the total, and the eighth digit from the right (in this case the leftmost digit) adds 128 to the total. Every digit in between adds 0 to the total, so we have 128 + 0 + 0 + 0 + 0 + 0 + 0 + 1 = 129