Is it possible to have an adjustable resistor?
If you ask that question, then you have just thought up of Potentiometers. A potentiometer is simply a variable resistor that can be controlled by the user. Potentiometers accomplish this by having three terminal resistors forming and a load that connect the potentiometer and the voltage source in one loop and the potentiometer and the load in another. Potentiometers have a wide range of uses, ranging from CD players to Servo mechanisms.