The following circuit is known as a Wheatstone bridge, or simply a bridge. It is

Question

The following circuit is known as a Wheatstone bridge, or simply a bridge. It is a very common measurement circuit, used with strain gauges, thermistors, and other devices whose resistance changes in response to something that you'd like to measure. Let's assume that each resistor in this circuit are 100 Ohm strain gauges. The resistance of these gauges changes slightly when you stretch or compress them. They are glued to a material (often steel) and are used to measure deformations of the material (called strain). Due to deformation, R1 and R4 decrease by 1% and R2 and R3 increase by 1%. Find Vab Due to a temperature change, the resistance of all gages increases by 5%. Find the percentage change in vab.

Explanation / Answer

R1 =R4 = 101 ohm

R2 = R3 = 99ohm

now R1 and R2 are is series

so equivalent = 200

similarly R3 and R4 equivalent = 200

so total equivalent resistance = 200/2 = 100ohm

total current = 10/100 = 0.1A

so the current in individual branch = 0.05

so 10 - 0.05*99 =Va

Va = 5.05V

similarly 10-0.05*101 = 4.95

so Vab = 0.1V

b) if all resistances increases equally

still the potential will be 0V because the balance condition of wheatstone bridge is still satisfied

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