# A copper metal wire is used as a strain gauge.

*label*Other

*timer*Asked: Aug 18th, 2015

**Question description**

- A copper metal wire is used as a strain gauge. The resistivity is 1.68x10
^{-8}Ω.m at 20. The length and cross-sectional area of the wire are 5mm and 4*10^{-4}m^{2}. The material elongates by an amount of 0.2mm in 0.2mm increments until it reaches 6mm in length. Assuming the*volume*remains constant, calculate the resistance at each length. You should use the standard equation for the resistance of a metal. What is that equation? Fill in the table below. Show all calculations. Calculate the difference in resistance between the resistance at each length and the resistance before strain is added. Also, calculate the change in resistance using the approximation found in equation 5.12 of your text. How does the change in length change the resistance of the gauge? Is it linear? Why or why not? (You can use Excel to create a plot and paste it in your submission if you want?) How good is the approximation?

Length | Cross-sectional area | Resistance | Initial resistance (at 5mm) | Change in the resistance | Change in resistance using Eq.5.12 |

5mm | |||||

5.2mm | |||||

5.4mm | |||||

5.6mm | |||||

5.8mm | |||||

6mm |