Deriving Electric Charge: Line, Ring, Cylinder, Cone, Sphere & Shell

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SUMMARY

This discussion focuses on deriving the electric charge formulas for various geometries: cylinder, cone, sphere, and shell, without using Gauss's Law. The user, Chris W, has successfully derived formulas for an infinite line of charge, semi-infinite line of charge, ring of charge, semi-ring of charge, disk of charge, and infinite sheet of charge. The key insight is that the ring of charge serves as the foundational element for deriving the formulas for the remaining geometries. The discussion emphasizes the importance of setting up the appropriate integrals in cylindrical and spherical coordinates.

PREREQUISITES
  • Understanding of electric charge and its distribution
  • Familiarity with integral calculus
  • Knowledge of cylindrical and spherical coordinate systems
  • Basic concepts of electrostatics
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  • Study the derivation of electric charge for a cylinder using cylindrical coordinates
  • Explore the derivation of electric charge for a cone using spherical coordinates
  • Learn how to derive the electric charge for a sphere and shell using integral calculus
  • Review the application of Gauss's Law in electrostatics for comparison
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Chris W
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Hi all. I need some help.
Without using Gauss's Law, I have to derive the formula for the electric charge for different cases.
-I already did few cases such as:
1. Infinite line of charge
2. Semi - infinite line of charge
3. Ring of charge
4. Semi - Ring of charge or any arc of charge
5. Disk of charge
6. Infinite Sheet of Charge

-I need to derive:
7. Cylinder of charge
8. Cone of charge
9. Sphere of charge
10. Shell of Charge

I know that the basic "building block" for cases 7-10 is the ring of charge which I already have. Basically what I need is the setup of the integral for cases 7-10.

Thank you

Chris W
 
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It's just an exercise in different coordinates. A cylinder has constant r, varying z and phi/theta in cylindrical coordinate, a cone has varying z, r and phi/theta in cylindricalm a sphere has varying, r, phi, theta in spherical and a shell has constant r, varying phi, theta in spherical
 
Thanks!

Yeah. Looks like I have all I need now I just have to set up the integrals.

Thanks! wow that was quick ... lol


please see what I have so far ... I hope all is good!

Thank you one more time

see attachment
 

Attachments

  • Infinite line of charge.jpg
    Infinite line of charge.jpg
    16.8 KB · Views: 567
  • Semi- infinite line of charge .jpg
    Semi- infinite line of charge .jpg
    17.7 KB · Views: 617
  • ring of charge.jpg
    ring of charge.jpg
    17.2 KB · Views: 554
this is the rest of what I have so far

sheet of charge can be viewed as the disk of charge and letting the R go to the infinify
 

Attachments

  • disk of charge page 1of2.jpg
    disk of charge page 1of2.jpg
    17.9 KB · Views: 359
  • disk of charge page 2of2.jpg
    disk of charge page 2of2.jpg
    20.6 KB · Views: 360
  • semi-ring or arc of charge.jpg
    semi-ring or arc of charge.jpg
    20 KB · Views: 346

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