## Resistor

### What is mean by resistor?

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses. A conductor has low resistance, while an insulator has much higher resistance. But every resistor has a fixed value of resistance that would have printed as a color code or in other methods.

### What is Resistance?

Before looking at what resistance is, it is necessary to understand a little about current and what it is. Essentially a flow of current in a material consists of a movement of electrons in one direction. In many materials there are free electrons moving about randomly within the structure. While these move randomly there is no current flow, because the number moving in one direction will be equal to the number moving in the other. Only when a potential causes a drift in a particular direction can a current be said to flow.

Resistance is a measure of the opposition to current flow in an electrical circuit.

Resistance is measured in ohms, symbolized by the Greek letter omega (Ω). Ohms are named after Georg Simon Ohm (1784-1854), a German physicist who studied the relationship between voltage, current and resistance. He is credited for formulating Ohm's Law.

### Ohm's Law

Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points.

$$\mathsf{V=IR}$$

$\mathsf{V}$ - Voltage.
$\mathsf{I}$ - Current.
$\mathsf{R}$ - Resistance.

In circuit analysis, three equivalent expressions of Ohm's law are used interchangeably as mentioned below:

$$\mathsf{ R=\frac{V}{I} \;\; {\text{ or }} \;\; V=IR \;\; {\text{ or }} \;\; I=\frac{V}{R} }$$

The interchangeability of the equation may be represented by a triangle as shown figure to easy memorize. Where $\mathsf{V}$ (voltage) is placed on the top section, the $\mathsf{I}$ (current) is placed to the left section, and the $\mathsf{R}$ (resistance) is placed to the right. The line that divides the left and right sections indicates multiplication, and the divider between the top and bottom sections indicates division (hence the division bar).

### Schematic symbols of a resistor

The Schematic symbol of resistor is represented by two types. The one with zigzag lines, and another with a rectangular box are shown in figure. 