# Homework Help: Wheatstone Bridge Calculation

1. Sep 9, 2011

### loobloke

1. The problem statement, all variables and given/known data
A strip of high-strength steel has a length of 30 cm and a cross section of 1 mm by 20 mm. The modulus of elasticity is 200 GPa, and Poission's ratio is 0.25. It is subjected to an axial load of 15,000N. It is instrumented with two axial strain gauges with R=159Ω and a gauge factor of 2.02. These two gauges are connected into opposite legs of a Wheatstone bridge (R1 and R3). The two fixed resistors are also 159Ω, and the supply voltage is 3.4V. The bridge is adjusted to zero-voltage output before the load is applied.
Find the output of the bridge with the load applied.

2. Relevant equations
Hooke's Law
Wheatstone Bridge Equation for Strain

3. The attempt at a solution
I've used the cross sectional area and Hooke's Law to find the strain. From then I just sub it into the wheatstone bridge equation?

However extra information is given so I'm afraid I might be missing something out.
We are applying axial load and measuring axial strain so possion's ratio is irrelevant. Likewise the length of the beam is also irrelevant then. Am I correct in thinking this?

Thanks.