Current through a Resistor learning electronics lesson 0001

The amount of current a resistor passes is based on the voltage across it. The amount of voltage in volts, is divided by the resistance in Ohms. That gives you the current in Amps.

Current through a resistor illustrated and schematic with calculations diagram by electronzap
Current through a resistor illustrated and schematic with calculations diagram by electronzap

Symbols for formula calculations.

  • I = Current
    1. Unit: Amp (A)
  • V = Voltage
    1. Unit: Volt (V)
  • R = resistance.
    1. Unit: Ohm (Ω)



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Ohms law formula for current: I=V/R

Current in (Amps) through a resistor, is the voltage across it (in volts), divided by it’s resistance (in ohms). I = V/R

Some other examples.

  • 100 ohm resistor with 1V across it will pass 1V/100Ω = 0.01A. Which is 10mA.
    • That will produce 1V x 0.01A = 0.01W of power.
  • 100 ohm resistor with 3V across it will pass 3V/100Ω = 0.03A.  Which is 30mA.
    • That will produce 3V x 0.03A = 0.09W of power.

Most resistors are rated to dissipate 1/4W (0.25W) maximum. However, it is still recommended to keep the wattage of a 1/4W resistor below half of that. So, below 1/8W (0.125W).

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