CHAPTER 19. ELECTRIC CIRCUITS 19.5
2.
1 Ω
2 Ω
4 Ω
6 Ω
3.
2 Ω
2 Ω
4 Ω
4 Ω
2 Ω
2 Ω
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19.5 Wheatstone bridge ESBIO
Another method of finding an unknown resistance is to use a Wheatstone bridge. A Wheatstone
bridge is a measuring instrument that is used tomeasure an unknown electrical resistance by
balancing two legs of abridge circuit, one leg of which includes the unknown component. Its
operation is similar to the original potentiometerexcept that in potentiometer circuits the meter used
is a sensitive galvanometer.
FACT
The Wheatstone bridge
was invented by Samuel
Hunter Christie in 1833
and improved and pop-
ularised by Sir Charles
Wheatstone in 1843.
R 3 R 1
R 2 Rx
V
�
� �
�
A
B
C
D Circuit for Wheatstone bridge
In the circuit of the Wheatstone bridge, Rxis the unknown resistance. R 1 , R 2 and R 3 are resistors of
known resistance and the resistance of R 2 is adjustable. If the ratioof R 2 :R 1 is equal to the ratio of
Rx:R 3 , then the voltage between the two midpoints will be zero and no current will flow between
