Resistors

Basic Electricity

  • Question 1

    Shown here is the schematic symbol for a resistor:



    What is the purpose of a resistor? What function does it perform? Also, draw an illustration of what a real resistor looks like.

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  • Question 2

    Resistors are sometimes represented in electrical and electronic schematic diagrams by a symbol other than this:



    Draw this other symbol next to the one shown above.

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  • Question 3

    A primitive resistor may be formed by sketching a thick line on a piece of paper, using a pencil (not an ink pen!):



    How may the end-to-end electrical resistance of this pencil mark be increased? How may it be decreased? Explain your answers.

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  • Question 4

    When a resistor conducts electric current, its temperature increases. Explain how this phenomenon is significant to the application of resistors in electric circuits. In other words, why would we care about a resistor’s temperature increasing?

    Also, what does this indicate about the technical ratings of resistors? Aside from having a specific resistance rating (i.e. a certain number of ohms), what other rating is important for proper selection of resistors in electric circuits?

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  • Question 5

    Many resistors have their electrical resistance shown by a set of color codes, or “bands,” imprinted around their circumference. A standard color code associates each color with a specific decimal digit (0 through 9). Associate each of the following digits with its respective color:

    0 =
    1 =
    2 =
    3 =
    4 =
    5 =
    6 =
    7 =
    8 =
    9 =
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  • Question 6

    Observe the following “4-band” resistors, their color codes, and corresponding resistance values (note that the last color band is omitted, since it deals with precision and not nominal value):



    What patterns do you notice between the color codes (given as three-letter abbreviations, so as to avoid interpretational errors resulting from variations in print quality), the resistance values, and the physical sizes of the resistors?

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  • Question 7

    What does the last color band represent on a color-coded resistor?

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  • Question 8

    Determine the nominal resistance values of these resistors, given their band colors, and also express the allowable tolerance in ohms.

    For example, a 25 kΩ resistor with a 10% tolerance rating would have an allowable tolerance of /- 2.5 kΩ.

    • Red, Org, Blu, Gld =
    • Brn, Blk, Grn, Sil =
    • Blu, Blk, Brn, Gld =
    • Yel, Vio, Red, Sil =
    • Grn, Brn, Yel =
    • Wht, Blu, Blk, Sil =
    • Gry, Grn, Org, Gld =
    • Org, Org, Gld =
    • Vio, Red, Sil, Gld =
    • Brn, Red, Blk, Sil =
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  • Question 9

    Observe the following “5-band” precision resistors, their color codes, and corresponding resistance values (note that the last color band is omitted, since it deals with precision and not nominal value):



    What patterns do you notice between the color codes (given as three-letter abbreviations, so as to avoid interpretational errors resulting from variations in print quality) and the resistance values of each resistor? Why do precision resistors use a “5-band” color code instead of a “4-band” color code?

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  • Question 10

    Determine whether or not the following resistors measure within the resistance range specified by their color codes:

    • (Org, Org, Red, Blk, Blu) Measured resistance = 332.5 Ω
    • (Brn, Blk, Blk, Gld, Red) Measured resistance = 9.7 Ω
    • (Blu, Vio, Brn, Red, Grn) Measured resistance = 67.43 kΩ
    • (Red, Wht, Grn, Yel, Vio) Measured resistance = 2.949 MΩ
    • (Yel, Vio, Org, Gld) Measured resistance = 44.68 kΩ
    • (Gry, Red, Brn, Sil) Measured resistance = 905 Ω
    • (Grn, Blu, Gld) Measured resistance = 6.73 Ω
    • (Vio, Brn, Red, Gld, Brn) Measured resistance = 70.82 Ω
    • (Wht, Org, Blu, Brn, Grn) Measured resistance = 9.38 kΩ
    • (Red, Blk, Wht, Grn, Vio) Measured resistance = 20.86 MΩ

    Assume that all five-band resistors listed here use the precision color code as opposed to the military 5-band code where the fifth band indicates resistor reliability.

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  • Question 11

    Find one or two real resistors and bring them with you to class for discussion. Identify as much information as you can about your resistors prior to discussion:

    • Resistance (ideal)
    • Resistance (actual)
    • Power rating
    • Type (carbon composition, metal film, wire-wound, etc.)
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