Integrating Non-Constant Charge Density in a Volume: Tips and Tricks

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Homework Help Overview

The problem involves calculating the total charge within a specified volume, given a non-constant charge density function that depends on multiple variables. The charge density is defined as \(\rho_v=10z^2\rho^{-0.1x}\sin(y\pi)\) over the ranges \(-1\leq x\leq 2\), \(0\leq y\leq 1\), and \(3\leq z \leq3.6\).

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the need to integrate the charge density over the specified volume and express concerns about the complexity introduced by the non-constant term \(\rho^{-0.1x}\). There are questions about potential substitutions and integration techniques, including the possibility of using integration by parts or consulting integral tables.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the charge density and its implications for integration. Some suggest that the integral may not be as complicated as it appears if \(\rho\) is treated as a constant, while others express confusion about the notation and the nature of the variables involved.

Contextual Notes

There is uncertainty regarding the interpretation of \(\rho\) in the context of the problem, with some participants questioning whether it should be considered a constant or a variable. The complexity of the charge density function, which involves both Cartesian and cylindrical variables, is also noted as a point of confusion.

stargoo
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Homework Statement


Find the total charge inside the volume indicated:
[tex]\rho_v=10z^2\rho^{-0.1x}\sin(y\pi) for -1\leq x\leq 2,0\leq y\leq 1,3\leq z \leq3.6[/tex]

I know I have to integrate over the volume [tex]dxdydz[tex], but [tex]\rho^{-.1x}[tex]just keeps giving me a problem. Is there a substitution that I'm missing here. Integrating by parts just gives a more complicated integral. I've tried converting [tex]\rho[tex]to [tex]\sqrt{x^2+y^2}[tex], but that doesn't help either. Any help would be appreciated.[/tex][/tex][/tex][/tex][/tex][/tex][/tex][/tex]
 
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got this from google [integral] b^{x} dx = b^{x} / ln(b) + C

Simple: look in integral tables :P
 
that would be all well and good, except that rho is not a constant in this case. The charge density in the stated problem is a function of cartesian AND cylindrical variables. Hence, my problem.
 
oops, I couldn't read properly the question..

It seems a real big mess to me ><
 
thanks for trying, though!
 
Are you sure rho is not a constant? The way I read the problem is rho(sub-v) represents some total charge (although that notation would seem a bit unconventional) defined as a function of x, y, z, and some undeclared (but constant) rho. From that point of view, the integral really isn't as ugly as it looks. The triple integral is performed by integrating with respect to one variable at a time, holding the others constant. Your final answer will just be in terms of rho.
If rho were variable, then you have a variable defined as a function of its anti-derivative, which is a differential equation, and you have a mess on your hands.
Good Luck!
 

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