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I R  RI  0 (1.2)
1 3 2 2
then

I R  I R  R R
1 X 2 1 X 1
   (1.3)
I R  I R R R
1 3 2 2  3 2

To determine zero current with a galvanometer, it can be done

with the extremely high accuracy. Therefore, if R ,R ,R are known to
1 2 3
high precision, then R can be measured to high precision as well.
X
R
R  R  1 (1.4)
X 3
R
2
In many cases the measurement of the unknown resistance is
related to the measurement of some physical values (such as force,
temperature, pressure, etc.) which thereby allow us to use Wheatstone

bridge to measure these values indirectly.
2. The Slidewire Wheatstone Bridge
For a "student" form of the bridge, there is a slidewire one, this
is a 1-meter long slide wire of low resistance. One terminal of the

galvanometer, connecting to a sliding tap key, can make an electrical
contact with this wire at any point along its length. The second
terminal is connected to the junction D. Moving the sliding tap key

along the slideware BC we can set the bridge in the state of balance (
galvanometer V should be zero). In this case
G
R
R  R  1 (2.1)
X 0
R
2
where R is a resistor of known the resistance (instead of R in
0 3
Fig. 1 and in formula (1.4)).
So resistance of the slidewire is proportional to its length,

therefore ratio of resistances R , R is respectively equal to ratio of l
1 2 1
and l and so
2
l
R  R  1 (2.2)
X 0
l
2
In practice R is precision resistance box (a box containing a
0
number of precision resistors connected to panel terminals or contacts,

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