Electrostatics - Coulomb's Law

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Discussion Overview

The discussion revolves around the derivation and understanding of the formula for the electric field (dE) in the context of Coulomb's Law as presented in Griffith's Electrodynamics book. Participants explore the role of the cosine function in the formula and the expectations regarding its derivation.

Discussion Character

  • Technical explanation, Conceptual clarification, Homework-related

Main Points Raised

  • One participant seeks clarification on the origin of the cos(theta) term in the formula for dE.
  • Another participant claims to have resolved the question by explaining that the r_hat vectors lead to a factor of 2(z/r)z_hat, where z/r equals cos(theta), resulting in 2cos(theta)z_hat.
  • A participant expresses concern about the difficulty of deriving the formula independently.
  • A later reply indicates that the formula is provided in a general form, suggesting that derivation is not solely the responsibility of the student.

Areas of Agreement / Disagreement

The discussion includes both agreement on the existence of the formula and differing views on the expectations for deriving it. Some participants find the derivation challenging, while others clarify that the formula is given.

Contextual Notes

Participants do not fully explore the assumptions behind the derivation or the implications of the cosine term, leaving some aspects of the discussion unresolved.

Who May Find This Useful

Students studying electrostatics, particularly those using Griffith's Electrodynamics, may find this discussion relevant for understanding the derivation of electric field formulas and the expectations surrounding them.

jinksys
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I'm doing example 2.1 in Griffith's Electrodynamics book. Can someone explain where the cos(theta) comes from in the formula for dE? The formula is on the first image: Here.
 
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SOLVED:

I see what's going on. If you add the r_hat vectors you end up with 2(z/r)z_hat. z/r=cos(theta). So we end up with 2cos(theta)z_hat.
 
that looks so hard. are you supposed to figure out that formula all by yourself
 
bael said:
that looks so hard. are you supposed to figure out that formula all by yourself

No, the formula is given to you in a general form.
 

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