Potentiometer Circuit Diagram
This is the basic circuit diagram for the simplified potentiometer (a.k.a. a really simple pH meter).
Parts Needed:
A. a cell that produces an electromotive
force (emf)
B. a cell that produces an electromotive
force (emf)
C. a battery
D. a variable resistor
E. a double throw switch
F. a movable contact
G. a galvanometer
H. a key
IJ. a resistance wire
How does it work?
Circuit 1contains the battery C, the adjustable resistance D, and the entire length of the resistance wire IJ
Circuit 2 contains the galvanometer G, the variable
length of resistance wire IF, the double throw switch E,
the key H, and either the cell A (the standard
cell) or the cell B (the cell of unknown potential) Which cell is
determined by the position of the double throw switch
E.
At this point I haven't explained
how the cells A or B produce a voltage, but for now just assume that A
(the reference) has an emf of 1 volt and B (the unknown) has an unknown
emf.
The basic idea is as follows:
The Galvanometer acts as a null detector
for voltage. This basically means that the galvanometer can detect whether
2 voltages are equal. In the current setup (no pun intended), the galvanometer
is used to detect a potential difference between Circuit 1 and Circuit
2. If there is no difference, the galvanometer will not be deflected.
If there is a difference, the galvonometer will be deflected.
Why? A galvanometer detects current. If the two circuits
are of the same potential, there will be no current (remember: current
occurs when there is a flow of charge from a region of high potential to
a region of low potential.