Resistor limiting current – Ohms law

The primary thing that resistors do is limit current (moving charges). The current (I) in amps through a resistor depends on the voltage (V) across the resistor divided by the resistor’s resistance (R) in ohms. I = V/R

Illustrated current through resistors diagram by electronzap electronzapdotcom
Illustrated current through resistors diagram by electronzap electronzapdotcom

Check out the Resistor component page if you are completely unfamiliar with resistors.

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Always keep in mind that while passing current, resistors get hot. The recommended maximum wattage rating of most resistors is 1/4W, which is recommended to be kept below 1/8W as much as possible.  Calculating the wattage (P) in watts, of any component, involves taking the voltage (in Volts) across it and multiplying it by the current (in Amps) flowing through it. P = VI

Multimeter placement for measuring voltage resistance current schematic and Current Voltage IV linear relationship diagram by electronzap electronzapdotcom
Multimeter placement for measuring voltage resistance current schematic and Current Voltage IV linear relationship diagram by electronzap electronzapdotcom

Usually schematic diagrams will show a safe resistor value to use. Review simple schematic diagrams often as part of the learning electronics process.

Great component/complete learning electronics kit.

Ohms law formula for current

  • I = V/R (current equals voltage divided by resistance). Ohms law formula for current from a certain voltage and resistance.
  • Voltage (V) across the resistor.
  • Current (I) flows through the resistor.
  • Current has a linear relationship (straight line on a graph) to resistance for a given voltage. Assuming that the voltage stays the same. Using half the resistance will double the current. Twice the resistance will result in half the current.
Ohms law voltage current resistance circle graph diagram by electronzap electronzapdotcom
Ohms law voltage current resistance circle graph diagram by electronzap electronzapdotcom

Common values diagram

Introduction to through hole 100 220 470 1K ohm resistor components color code electrical properties diagram for video by electronzap electronzapdotcom
Introduction to through hole 100 220 470 1K ohm resistor components color code electrical properties diagram for video by electronzap electronzapdotcom
  • The three lines on the right side of the resistor indicates 0V ground (negative side of a DC supply).
  • The voltage on the left side of the resistor indicates the supply voltage (positive side of DC supply).
  • The supply voltage (Vcc) and 0V ground is the voltage difference across the resistor.  For example 5V and 0V has a 5 volt difference. There is 5V across that resistor.
  • 1/4W (0.25W)  maximum is a common value resistor. It is still recommended to keep them below 1/8W (0.125).
  • Be aware that any other components in series with the resistor will drop (semiconductor) or divide (resistive) voltage from the resistor.

Detailed video

Clicking the links to watch videos directly on YouTube helps a lot!

Electronics course 1 Resistor component limiting current Ohms law and multimeter measurements

Diagram used in video
Basic electronics circuit fragments and simple circuits 1 diagram covering resistors ohms law and multimeter measurements by electronzap electronzapdotcom
Basic electronics circuit fragments and simple circuits 1 diagram covering resistors ohms law and multimeter measurements by electronzap electronzapdotcom
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