# Introduction to Resistors

the very basic definitions:

## What is Electrical Resistance ?

Physical property in conductor or of a component which transforms electrical energy into heat

## What is Electrical Resistor ?

Resistors are passive electrical components that limits the flow of electric current.

Component R that has no significant distortion of phase at an applied voltage U and the resulting flow of current I

Resistors, like inductors and capacitors, are passive electronic components which are quite simple in theory but rather more complex when the behaviors of real-world devices are considered. Any resistor that one can build or buy is non-ideal in some respect that renders it unsuitable for some purposes; the various products available offer different balances of imperfection in an effort to be found good enough for others..

Resistors can be found in almost all electrical networks and electronic circuits. The resistance is measured in ohms. An ohm is the resistance that occurs when a current of one ampere passes through a resistor with a one volt drop across its terminals. The current is proportional to the voltage across the terminal ends. This ratio is  represented by Ohmâ€™s law:

where U= applied voltage; R= resistive value; I= resulting current

Despite the Ohms’ law is one of the most frequent used relationship for components and circuits, there is some limitation for it validity at:

• high frequencies (relaxation, skin effect)
• high field strengths (flashovers at highly resistive materials)
• very low temperatures (superconductivity)

Resistors have several properties besides their rated resistance, such as their temperature coefficient, resistor noise and power rating. These resistor properties can be important to take into account depending on the application.

Resistors are used for many purposes. A few examples:

• delimit electric curren
• tvoltage division
• heat generation
• control gain
• fix time constants
• current measurements

They are commercially available with resistance values over a range of more than nine orders of magnitude. They can be used to as electric brakes to dissipate kinetic energy from trains, or be smaller than a square millimeter for electronics.

Resistor technologies differ in features, range of electrical parameters covered. Lets start our course to learn some basics about them and what technologies are available today.

There are number of videos that you can find on YouTube etc. about basic introduction of resistors and analogy with water etc. We would like to dig a little deeper during this course into how resistor works, what are the physical mechanisms and background. Nevertheless, you can immerse into the resistor world now to start watching this introduction video.

Optional video, 6:30 min, source: EEPower

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