# The gauge factor is defined as:

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The gauge factor is defined as:
1. $\frac{{\Delta L/L}}{{\Delta R/R}}$
2. $\frac{{\Delta R/R}}{{\Delta L/L}}$
3. $\frac{{\Delta R/R}}{{\Delta D/D}}$
4. $\frac{{\Delta R/R}}{{\Delta P/P}}$

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Correct Answer - Option 2 : $\frac{{\Delta R/R}}{{\Delta L/L}}$

Gauge Factor:

The gauge factor is defined as the ratio of per unit change in resistance to per unit change in length. It is a measure of the sensitivity of the gauge.

Gauge factor, ${G_f} = \frac{{{\rm{\Delta }}R/R}}{{{\rm{\Delta }}L/L}}$

$\frac{{{\rm{\Delta }}R}}{R} = {G_f}\frac{{{\rm{\Delta }}L}}{L} = {G_f}\varepsilon$

Where ε = strain = $\frac{{\Delta L}}{{L}}$

The gauge factor can be written as:

= Resistance change due to change of length + Resistance change due to change in the area + Resistance change due to the piezoresistive effect

${G_f} = \frac{{{\rm{\Delta }}R/R}}{{{\rm{\Delta }}L/L}} = 1 + 2v + \frac{{{\rm{\Delta }}\rho /\rho }}{\varepsilon }$

If the change in the value of resistivity of a material when strained is neglected, the gauge factor is:

${G_f} = 1 + 2v$

The above equation is valid only when the Piezoresistive effect that changes in resistivity due to strain is almost neglected.

For wire-wound strain gauges, Piezoresistive effect is almost negligible.