الفيزياء العامة الجزء الثاني#موقع الفيزياء.كوم

8.7.2 The Wheatstone Bridge
Lectures in General Physics
This is a circuit consist of four resistors, emf, and galvanometer. The
Wheatstone bridge circuit is used to measure unknown resistance. In figure
8.25 show three resistors R 1 , R 2 , and R 3 are known with R 1 is a variable
resistance and resistor R x is the unknown one.
R 1
R 2
I 1
I 2
ξ
a
G
b
R 3
R x
Figure 8.25
To find the resistance R x the bridge is balanced by adjusting the variable
resistance R 1 until the current between a and b is zero and the galvanometer
reads zero. At this condition the voltage across R 1 is equal the voltage
across R 2 and the same for R 3 and R x . Therefore,
I 1 R 1 = I 2 R 2
I 1 R 2 = I 2 R x
Dividing the to equation and solving for R x we get,
R
R
2 3
R x
= (8.23)
R1
This shows how unknown resistor can be determined using the Wheatstone
bridge.
Dr. Hazem Falah Sakeek