• Resistance determines how much current will flow through a material.
  • They are components which oppose the flow of electrical current.
  • Resistors placed in series yield a total resistance that is equal to the sum of the resistances of the individual resistors:Total Resistance in Series
  • The more components that are placed in parallel the less the resistance in a circuit. Resistors in parallel yield a resistance that can be calculated using the following formula:
    • Total Resistance in Parallel
  • A variable resistor is a resistor whose value can be varied between its minimum and maximum values:
    • I am unsure how low this minimum value is but judging from how this component works as well as data from Yenka I believe that the minimum value should be near or at 0Ω.

Pull-Down, Pull-Up:

  • A pull-down resistor ensures that an IC does not accidentally register a false high reading.
  • A pull-up resistor ensures that an IC registers the full voltage of the battery and registers as high:
    • An example of this can be found connected to pin 2 of a 555IC in monostable mode.


  • Resistors all have different tolerances:
    • If the tolerance band is gold then the resistance is within the ±5% of the marked value:
      • This is important in circuits whose performances are dependent upon the accuracies the resistors within:
        • A clock or timer using an astable circuit to keep time.
  •  Resistor without a tolerance band generally has a tolerance of ±20%.

Preferred Values:

  • The most popular resistor ranges are the E12 and E24 ranges.
    • They take into account the manufacturing tolerances and are chosen such that there is a minimum overlap between the upper possible value of the first value and in the series and the lowest possible value of the next.
      • Hence there are fewer values in the E12 range which deals with resistors with a tolerance of ±10%.
  • E12 (±10%):
    • 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82
  • E24 (±5%):
    • 10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91
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