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Laboratory work #39
THE DETERMINATION OF THE UNKNOWN ELECTRICAL
RESISTANCE BY WHEATSTONE BRIDGE
Aim of work: to develop the method of measurement of

unknown electrical resistance by Wheatstone bridge
Laboratory equipment: laboratory bench of Wheatstone bridge
1. Wheatstone bridge

Wheatstone bridge is an electrical circuit used to measure an
unknown electrical resistance by balancing two legs of a bridge
circuit, one leg of which includes the unknown component R .
X

Figure 1.1

In Fig. 1 R the unknown resistance is measured; R ,R ,R are
X 1 2 3
resistors of the known resistance value. If the voltage between the two

midpoints (A and D) is zero and there is no current flow through the
galvanometer V , then the bridge is in the state of balance. When the
G
bridge is balanced, then I = 0, the second Kirchhoff's rule for loops
G
ABDA and ADCA can be rewritten as:

I R  RI  0 (1.1)
1 X 2 1

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