The correct answer is: E. all of the above
A potentiometer is a three-terminal resistor with a sliding contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat. If an external voltage source is applied to the input terminals, the current through the resistor will vary as the wiper is moved along the resistor element.
Potentiometers are commonly used to create voltage references, to measure resistance (as part of a Wheatstone bridge), and to control electrical devices such as volume controls or light dimmers. They can also be used to calibrate ammeters and voltmeters.
A potentiometer can be used to measure resistance by connecting it to a voltage source and a known resistor. The voltage across the known resistor is then compared to the voltage across the potentiometer. The ratio of these two voltages is equal to the ratio of the resistances of the two resistors.
A potentiometer can be used to measure current by connecting it in series with a known resistor and a voltage source. The current through the circuit is then equal to the voltage across the known resistor divided by the resistance of the potentiometer.
A potentiometer can be used to calibrate ammeters and voltmeters by connecting it in series with the meter and a known resistor. The voltage across the known resistor is then adjusted until the meter reads the correct value.
In conclusion, a potentiometer can be used for a variety of purposes, including measurement of resistance, measurement of current, calibration of ammeters, and calibration of voltmeters.