Why materials oppose charge flow and how resistance turns electrical energy into heat.
What is resistance?
Resistance is the ratio between voltage and current for an ideal ohmic component: R = V/I.
It is measured in ohms.
At the microscopic level, moving charge carriers scatter from atoms, defects, vibrations and other carriers. Geometry and material determine the result.
What changes resistance?
Temperature, light, mechanical strain, magnetic fields and frequency can all affect resistance.
A metal often increases in resistance as it heats. A thermistor, photoconductor or strain gauge is designed to make such dependence useful.
Why is it important?
Resistance controls current, divides voltage, dissipates energy and helps circuits interact with sensors and loads.
It also limits fault current and converts electrical behavior into measurable heat or voltage.
Limits
Not every device obeys Ohm's law. Diodes, lamps, transistors and many materials have nonlinear or changing relationships.
Resistance is therefore a model of behavior under stated conditions, not a universal substance inside every component.
Ai disclosure: written with the help of AI (ChatGPT). You are encouraged to point out errors and omissions.  
