Find Potential of Disk of Radius R, Charge Q w/ Equ 1

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Homework Help Overview

The discussion revolves around finding the electric potential of a disk with radius R and total charge Q, focusing on using a specific equation (Equ 1) for the calculation instead of another (Equ 2). The original poster seeks clarification on the integration process involved in this context.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the integration of the electric field to determine potential, with the original poster attempting to set up the integral using Equ 1. Some participants question the correctness of the original poster's approach and clarify the need to first determine the electric field before proceeding with the potential calculation.

Discussion Status

The discussion is active, with participants providing guidance on the necessary steps to calculate the potential. There is a recognition of the need to correctly identify the electric field before applying the integration for potential. While there is some agreement on the general approach, no explicit consensus has been reached regarding the specific setup of the integrals.

Contextual Notes

Participants are navigating the complexities of integrating over a disk and the distinction between calculating electric potential and electric field. There is an emphasis on ensuring the correct application of the equations involved.

Miike012
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I would like to know if there is a way of finding the Potential of a disk of radius R and charge Q with uniform charge distribution using Equ 1 instead of Equ 2?

Equ 1:
ΔV = -∫Edotdx rather than

Equ 2:
ΔV = ∫dUelec potential

For Equ 1 I'm guessing that the equation would be of the form...

ΔV = -∫∫Ecos(∏/2)dA = -∫∫EdA = -∫∫Edxdy
And
Limits of int (X-Direction): -√(R2 - y2) to √(R2 - y2)
Limits of int (Y-Direction): -√(R2 - x2) to √(R2 - x2)

And E would be the EField of a disk...
 
Last edited:
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You can certainly integrate the E field to find the potential, but your attempt is wrong. It looks like you're confusing calculating the potential with calculating E.

To use equation 1, you need to have already found ##\vec{E}##, and you'd calculate the line integral along any path C that runs from infinity to the point ##\vec{r}##:
$$ V(\vec{r}) = -\int_C \vec{E}\cdot d\vec{x}.$$ To find ##\vec{E}##, you'd calculate the contribution from each piece of the disk to the electric field at some point in space, and then integrate over the entire disk.

To use equation 2, you take a similar approach as you do when calculating ##\vec{E}##. You calculate the contribution from each piece of the disk to the electric potential at some point in space, and then integrate over the entire disk. Calculating electric potential is a bit easier than calculating the field because the potential is a scalar quantity. You don't have to worry about summing vectors like you do when calculating the electric field.
 
vela said:
You can certainly integrate the E field to find the potential, but your attempt is wrong. It looks like you're confusing calculating the potential with calculating E.

To use equation 1, you need to have already found ##\vec{E}##, and you'd calculate the line integral along any path C that runs from infinity to the point ##\vec{r}##:
$$ V(\vec{r}) = -\int_C \vec{E}\cdot d\vec{x}.$$ To find ##\vec{E}##, you'd calculate the contribution from each piece of the disk to the electric field at some point in space, and then integrate over the entire disk.

So equation 1 would be..

V = -∫Ediskdx and integrate from xf = distance from point to disk and xi = ∞. is that correct?
 
Last edited by a moderator:
Yes, basically.
 

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