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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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## Discussions

"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.

ok but i don''t see how i can find the change in resistance.
let's say we have a circuit.

emf: 4.5V.

A resistor of resistance O is placed in series with the strain gauge and the dc supply is connected across them.
The voltage across resistor is V.
length of strain gauge is unknown(L)
how can it be done then when it is a under a strain.

forget about it i just got it.

OK.

Sometimes all you need to do is explain it to somebody else.

just forget about it i just got it now.
LOL!!!
this is funny i got the solution when i was reading an article on format wars on wikipedia.

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.