Potentiometer

Potentiometer

Potentiometer is a device that is equivalent to a circuit. It actually applies the same concept as that of
potential divider. Do you still remember the principle of potential divider? If not, please refer here.

Physically, this is how a potentiometer looks like ( one example):

Normally we use the variable resistor as the potentiometer to control the voltage. Before I explain any further, please refer Diagram 1 and Diagram 2 below:

Diagram 1: Potential Divider

                                 

Diagram 2: Potentiometer

If we could realize, both Diagram 1 & Diagram 2 are quite similar. In Diagram 2, we have that black thick wire of from A to B. As we know, the resistance of any wire is always directly proportional to wire which means that , the longer the wire the higher the resistance. 

l directly proportional with R

In the middle of wire AB, we have S. S is where we can control in order to get our desired resistance. The chosen amount of resistance is then contributes to the potential difference across voltage,Vout (measured by a voltmeter). S divides wire AB into portion AS and SB. Did you get this?? Remember l directly proportional with R, hence 

                                                                                    lAS = RAS

                                                                                       and 

                                                                                     lSB = RSB

Recally equation for voltage divider, 

VAB = RAB 

The purpose of a potentiometer is to determine the unknown value of emf or the unknown value of the internal resistance of the same source (emf). 

Referring to Diagram 2, if we replace Voltmeter (that measures Vout ) with a cell with unknown emf, we could apply equation __ to know the answer.  

Thank You, 

Mdm Ummi Atiah

KMPk

                                                                 ~ May it Benefits You ➽💕