Divergence theorem/vector calculus

Click For Summary
SUMMARY

The discussion centers on proving that the gradient dot product with the unit vector \( r \) equals \( \frac{2}{r} \). The user initially proposes that the result should be \( \frac{3}{r} \), derived from the expression of the unit vector \( r \) as \( \frac{r}{r} \) and calculating the gradient. However, a counterpoint is raised, emphasizing the dependency of \( r \) on the variables \( x, y, \) and \( z \), specifically noting that \( r = \sqrt{x^2 + y^2 + z^2} \).

PREREQUISITES
  • Understanding of vector calculus concepts, specifically the gradient operator.
  • Familiarity with unit vectors and their properties.
  • Knowledge of the divergence theorem and its applications.
  • Basic algebraic manipulation involving multivariable functions.
NEXT STEPS
  • Study the properties of the gradient operator in vector calculus.
  • Learn about the divergence theorem and its implications in physics and engineering.
  • Explore the derivation of unit vectors in three-dimensional space.
  • Investigate the relationship between scalar fields and their gradients.
USEFUL FOR

Students and professionals in mathematics, physics, and engineering who are studying vector calculus, particularly those focusing on the divergence theorem and gradient operations.

t_n_p
Messages
593
Reaction score
0

Homework Statement



I want to show that:

Grad dot product with r = 2/r

where:
r is the unit vector r/r
r = xi + yj + zk
r is magnitude of r

The Attempt at a Solution



I think the answer should be 3/r

since unit vector r = r/r,
r = (x/r)i + (y/r)j + (z/r)k

then when I do grad dot r I should get (1/r) + (1/r) + (1/r) = (3/r)

what do you think?
 
Physics news on Phys.org
I think you are ignoring the fact that r=sqrt(x^2+y^2+z^2) and so r depends on x, y and z.
 

Similar threads

  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
Replies
3
Views
2K
  • · Replies 10 ·
Replies
10
Views
1K
  • · Replies 3 ·
Replies
3
Views
1K
  • · Replies 5 ·
Replies
5
Views
3K
Replies
1
Views
2K
Replies
3
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K