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i need some help in this homework.

Foil length of strain gauge is L
Resistance of strain gauge is R
Equation is deltaR/R=0.485(deltaL/L)

the strain gauge is given a strain of X%.

The question says to calculate the change in resistance on the strain gauge.

My problem is that i don't understand the X% strain. I'm not asking for answer, just want to know what the X% strain means

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The forums are retiring in 2021 and are now closed for new topics and comments.

"Strain" is simply the proportion of deformation, usually stretch.

So, a strain of 5% means the sample has stretched by 5% of its original length.

When something is Strained pulled along ( say the X axis ) it gets longer
and thinner causing the resistance to increase.
That is what a strain gauge does and must be calibrated at rest before
measuring a mechanical stress.

I have torque of shaft strain gauge with slip rings to measure torque in a
rotating motor.

A

There are a few formulae on http://en.wikipedia.org/wiki/Strain_gauge

...not sure if they really help since your formula seems to have the factor built in.