Expand the quadratic term for resistance equation

In summary, when the length of a cylindrical wire is increased by x percent while the volume and resistivity remain the same, the resistance will change by approximately 2x percent. This can be calculated by expanding the quadratic term and ignoring the small (\frac x {100})^2 term.
  • #1
amcavoy
665
0
A cylindrical wire of length [itex]\ell[/itex] and cross-sectional area [itex]\textrm{A}[/itex] has a fixed volume [itex]\textrm{V}[/itex]. If [itex]\ell[/itex] is increased by [itex] +x [/itex] percent and the volume and resistivity stay the same, by what percentage (in terms of [itex]x[/itex]) will the resistance change?
I said that [itex]A\ell=A_{\textrm{new}}\ell\left(1+\frac{x}{100}\right)\implies A_{\textrm{new}}=\frac{A}{1+\frac{x}{100}}[/itex]. Also, we know that [itex]R\propto\frac{\ell}{A}.[/itex]. Therefore,

[tex]R_{\textrm{old}}\propto\frac{\ell}{A}[/tex]

[tex]R_{\textrm{new}}\propto\frac{\ell\left(1+\frac{x}{100}\right)^{2}}{A}[/tex]

Somehow I'm not getting as nice of an answer as I expected.
 
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  • #2
Expand the quadradic term, you can claim that the [itex] {(\frac x {100})}^2 [/itex] term is very small and ignore it. Can you see where to go from there?
 
  • #3
So roughly [itex]2x[/itex] percent?
 

What is the quadratic term in the resistance equation?

The quadratic term in the resistance equation refers to the term that is squared. In the case of the resistance equation, the quadratic term is the term that includes the velocity squared.

Why is it important to expand the quadratic term in the resistance equation?

Expanding the quadratic term in the resistance equation allows for a more accurate calculation of resistance. It takes into account the non-linear relationship between velocity and resistance, which is necessary for more precise calculations.

Can the quadratic term be ignored in the resistance equation?

No, the quadratic term should not be ignored in the resistance equation. Ignoring it will result in a less accurate calculation of resistance.

How do you expand the quadratic term in the resistance equation?

To expand the quadratic term in the resistance equation, you need to square the term that includes the velocity. Then, you can combine like terms and simplify the equation as needed.

What is the purpose of expanding the quadratic term in the resistance equation?

The purpose of expanding the quadratic term in the resistance equation is to account for the non-linear relationship between velocity and resistance. This allows for more accurate calculations and predictions in scientific experiments and engineering designs.

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