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Difficulty: MediumResistors and Potentiometers

An avionics technician is inspecting a four-band carbon composition resistor on a circuit board with the color band sequence: Red, Violet, Gold, and Gold. What is the nominal resistance and tolerance rating of this resistor?

  1. A
    270 Ω±5%270\ \Omega \pm 5\%
  2. 2.7 Ω±5%2.7\ \Omega \pm 5\%Answer
  3. C
    2.7 kΩ±5%2.7\text{ k}\Omega \pm 5\%
  4. D
    0.27 Ω±5%0.27\ \Omega \pm 5\%

Answer

The nominal resistance is 2.7 Ω2.7\ \Omega with a tolerance of ±5%\pm 5\%.
In standard four-band resistor color coding, Red represents 2, Violet represents 7, a Gold third band represents a multiplier of 0.10.1, and a Gold fourth band represents ±5%\pm 5\% tolerance. Calculating 27×0.127 \times 0.1 gives 2.7 Ω±5%2.7\ \Omega \pm 5\%.

Step-by-Step Solution

1
Decode the first two color bands into the significant digits.
The first band (Red) represents the digit 22, and the second band (Violet) represents the digit 77, forming the base number 2727.
Standard four-band EIA color codes use the first two bands for the primary significant figures.
2
Apply the multiplier value indicated by the third color band.
The third band is Gold, which indicates a multiplier factor of 10−110^{-1} (0.10.1). Multiplying gives 27×0.1=2.7 Ω27 \times 0.1 = 2.7\ \Omega.
When Gold appears in the multiplier band position, it denotes a decimal factor of 0.10.1 for low-resistance values.
3
Determine the tolerance percentage from the fourth color band.
The fourth band (Gold) designates a ±5%\pm 5\% manufacturing tolerance.
The fourth band identifies the allowable deviation from the nominal resistance value.

Key Concept

Four-Band Resistor Color Code with Fractional Multipliers
Estimated Time:40s
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Topics

Resistors and Potentiometers

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