Series resistors

Connecting resistors in series does a few things.

  • Increases resistance
  • Divides voltage
  • Spreads out heat dissipation

I assume you already know

Increased resistance

Series resistors always provide more resistance than any of their individual values.

Series resistors on a breadboard diagram by electronzap electronzapdotcom
Series resistors on a breadboard diagram by electronzap electronzapdotcom

Series resistors simply add up their resistance.  Two series 1KΩ resistors look like a 2KΩ to a multimeter or to other circuitry.

Three 1KΩ resistors connected in series have the equivalent of 3KΩ of resistance.

Voltage divider

Series components always split up/divide/drop voltage from the power supply unless they have 0Ω of resistance.

Equal series resistors split up supply voltage evenly scheatic diagram by electronzap electronzapdotcom
Equal series resistors split up supply voltage evenly scheatic diagram by electronzap electronzapdotcom

The series resistors divide up whatever voltage is given to them based on their percentage of the series circuit resistance.

Equal value resistors are easy to calculate. Two equal value series capacitors will have half the supply voltage across each of them.

Power sharing – Heat generation/dissipation

The diagram above shows how two series 100Ω resistors with 5 volts across them (2.5V each) will pass the same current as a 200Ω resistor with 5V across it. The wattage of each component is the voltage across it times the current through it. Since a 200Ω resistor with 5V across it will pass 0.025A, and 0.025A x 5V = 0.125W, it will be twice as hot as either of the two series 100Ω resistors.

Series resistors split up wattage demonstration with thermal images

Good topics to continue with
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