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Electronics Information for Armed Services Vocational Aptitude Battery (ASVAB) Study Guide (page 6)

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Updated on Jul 5, 2011

Testing Instruments

The testing of electronic circuits requires a few specialized test instruments. Measuring basic DC circuit parameters can be accomplished with the following instruments:

  • ammeter: measures currents
  • ohmmeter: measures resistance
  • voltmeter: measures voltage

Voltage is the easiest parameter to test. A voltmeter can easily be connected across the device being tested at any point in the current. An ammeter must be connected in series to give a true indication of the current in the circuit. An ohmmeter is typically used on an unpowered device to measure its resistance. Many times the device being measured must be completely removed from the circuit to get an accurate resistance measurement. Power in a circuit is typically calculated after measuring the voltage and current.

Testing AC circuits and digital circuits requires much more complex and expensive test equipment. An oscilloscope is used to display AC and complex voltage waveforms. It is an indispensable tool for analyzing most of the circuits found in today's electronic products. The test equipment needed to test tomorrow's circuits will become more and increasingly specialized with the continued rapid growth of technology.

Radio

The radio was invented by Guglielmo Marconi in the late 1800s.

The theory behind radio is simple; however, the experience needed to fully understand radio may take years of study to develop. The simple drawing below shows how radio communication works.

Radio

The voice or music signal is combined with a carrier wave and fed into an amplifier and then to an antenna. The antenna transmits the combined signal into the air. The receiving antenna catches the weak signal out of the air and sends it to an amplifier. The signal is amplified, and then the carrier wave is removed, leaving the original voice or music signal intact. The original signal can then be amplified again and listened to through a speaker.

Radio: communication between two or more points using electromagnetic waves as the transmission medium.

Radio communication was first used on ships to communicate at sea. The importance of radio was proven when assistance was requested by the Titanic when it was sinking. Radio communication is not limited to the AM and FM radios we listen to. Television and cellular phones are also examples of radio communication.

Practice Questions

Now use what you've learned to answer the following electronics questions. Answers are at the end of the chapter.

  1. An electrical device that can store an electrical charge is called a(n)
    1. fuse.
    2. battery.
    3. capacitor.
    4. ohm.
  2. How many electrons are there in four coulombs of charge?
    1. 13.1 × 1018
    2. 6.25 × 1018
    3. 6.25 × 10–18
    4. 2.5 × 1019
  3. Which of the following values would provide the greatest resistance?
    1. 1 k Ω
    2. 1 m Ω
    3. 1 u Ω
    4. 1 M Ω
  4. Electrical power is measured in
    1. watts.
    2. volts.
    3. current.
    4. capacitors.
  5. Which of the following is a statement of Ohm's law?
    1. I = middle
    2. P = V × I
    3. V = I × R
    4. P = I2 × R
  6. One of the reasons copper is used to make wires is because it is
    1. grounded.
    2. a very good conductor.
    3. difficult to find, therefore expensive.
    4. easy to shape.
  7. Carbon resistors are typically used when
    1. a large resistance is required.
    2. a small resistance is required.
    3. an exact resistance is required.
    4. cost is the most important consideration.
  8. A high tension power line has 100 amperes flowing through it. The resistance of the power line is .01 Ω/foot. How much power, in watts, is lost in one foot of wire?
    1. 1 watt
    2. 10 watts
    3. 100 watts
    4. 1,000 watts
  9. Electric current is measured in
    1. amperes.
    2. coulombs.
    3. watts.
    4. volts.
  10. Special "slo-blo" fuses are required when a circuit exhibits which characteristic?
    1. a short circuit
    2. in-rush current
    3. voltage fluctuations
    4. open circuits
  11. Which of the following is NOT an example of radio communication?
    1. AM radio
    2. cellular phones
    3. a tape recorder
    4. television
  12. Which electrical component allows current to flow in only one direction?
    1. a capacitor
    2. a resistor
    3. a diode
    4. a wire

Answers

  1. c. Since a capacitor can store an electrical charge, a common application for capacitors is protecting appliances from voltage spikes.
  2. d. One coulomb is 6.25 × 1018 electrons. Four times 6.25 × 1018 = 25 × 1018 = 2.5 × 1019.
  3. d. The multipliers are:   k × 1,000
                               m × .001
                                u × .000001
                               M × 1,000,000
  4. a. A watt is defined as the work done in one second by one volt to move one coulomb of charge.
  5. c. Ohm's law is V = I × R
  6. b. Copper is used to make most wires because it is an ideal conductor and it is relatively inexpensive.
  7. d. Resistors of all types can be made to have large or small resistances. Carbon resistors are used when cost is the most important consideration.
  8. c. P = I2 × R = (100 A)2 × .01 Ω = 100 watts.
  9. a. Electric current is measured in amperes.
  10. b. Regular fuses are used to protect against short circuits and voltage fluctuations. Open circuits do not need to be protected by a fuse.
  11. c. Tape recorders do not use electromagnetic waves as the transmission medium.
  12. c. A diode allows current to flow in one direction only.
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