R is proportionality coefficient and called resistance(electric resistance). Resistance volume code is R, unit code is Ω(ohm), and electronic symbol is expressed as below.
[Electronic symbols of resistor］
If the resistance is higher, the current will be difficult to flow, but easy to flow if the resistance is lower. In other words, resistor works to keep the current flowed to a circuit stable and to change it if necessary. Resistor also works to decrease the voltage or divide the voltage.
Resistor is thus indispensable product for one of the fundemental components of electric circuit, as capacitors and inductors.