Vector Calculus Problem - Griffith Textbook

Click For Summary

Discussion Overview

The discussion revolves around a vector calculus problem from the Griffith textbook, specifically Question 1.21, which involves interpreting the expression (A.∇)B. Participants explore the meaning of this expression and its implications in vector calculus, particularly in the context of electrodynamics.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests calculating the divergence of A and multiplying it by the components of B to find the x component of the expression, indicating a simplistic approach.
  • Another participant proposes that (A.∇)B represents the directional derivative, which describes how the field B changes in the direction of A.
  • A third participant clarifies that (A.∇)B and B(∇.A) are not equal, noting that the operator acts to the right, meaning B is differentiated in (A.∇)B while A is differentiated in B(∇.A).
  • A later reply expresses gratitude, indicating that the discussion has clarified the issue for them.

Areas of Agreement / Disagreement

The discussion shows some agreement on the interpretation of the expression (A.∇)B, but there are differing views on the approach to understanding it, particularly regarding the operations involved. The discussion remains somewhat unresolved as participants have not reached a consensus on the best method to interpret the expression.

Contextual Notes

Participants have not fully explored the implications of their interpretations, and there may be missing assumptions regarding the definitions of the operators involved. The discussion does not clarify all mathematical steps necessary for a complete understanding.

Bruce Dawk
Messages
3
Reaction score
0
I have a problem in the Griffith textbook (Introduction to Electrodynamics), Question 1.21, where it asks what is the meaning of the vector (A.∇)B, my simplistic approach would be to calculate the divergence of A which should be a scalar and multiply it out by Bx,By,Bz) to compute the x component of the expression. However in the solution manual (available by searching Introduction to Electrodynamics Solutions and clicking on the Scribd link) it seems to be the other way around.

I just don't understand why this is, can someone clarify please?
 
Physics news on Phys.org
(A.∇)B and B(∇.A) are not equal because that operator acts to the right so in
(A.∇)B
B is differentiated while in
B(∇.A)
A is differentiated
 
Thanks all. Its quite clear now.
 

Similar threads

  • · Replies 50 ·
2
Replies
50
Views
5K
  • · Replies 8 ·
Replies
8
Views
4K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 20 ·
Replies
20
Views
2K
Replies
2
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 12 ·
Replies
12
Views
3K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 16 ·
Replies
16
Views
6K