What does Griffith mean by this hint? [Electrodynamics]

In summary, the conversation discusses the modification of equation 7.5 due to the non-constant current density caused by the non-zero conductivity and charge density in a resistive medium. The use of the constitutive equation and continuity equation for stationary currents is suggested to modify the equation, with s possibly representing the cylinder coordinate in standard notation. The conversation also mentions the importance of posting such questions in the homework forum.
  • #1
Mind----Blown
11
0
I was solving the problems given by Griffith in his book 'Introduction to Electrodynamics' and stumbled across this question.
Screenshot_3.png
Screenshot_12.png

Screenshot_1.png

"Because sigma (conductivity of the medium) is a function of position, the equation 7.5 does not hold" --i get this point; current density isn't constant and so its divergence will be non zero.
"The charge density is non zero in the resistive medium"-- I have no clue what this sentence means.. I can't even think why i don't find it right.. someone please explain it to me!

Thanks a lot !
 
Physics news on Phys.org
  • #2
Another hint: Use the constitutive equation
$$\vec{j}=\sigma \vec{E}$$
and the continuity equation for stationary currents
$$\vec{\nabla} \cdot \vec{j}=0,$$
which together immediately tell you, how to modify Eq. (7.5). Also it would be helpful to tell, what ##s## is. Is it the cylinder coordinate ##r## in standard notation? I guess so from the Figure, which indicates that ##\vec{E}## is radially out.

PS: Questions like this should be posted in the homework forum!
 

1. What is the context of Griffith's hint in electrodynamics?

The hint is given in the context of electromagnetic theory and specifically in the section on Maxwell's equations. It is meant to provide a helpful hint for solving problems related to these equations.

2. What does Griffith mean by "this hint"?

"This hint" refers to a specific hint or tip given by Griffith in his book "Introduction to Electrodynamics." It is meant to guide readers in their understanding and application of electrodynamics concepts.

3. How can I use Griffith's hint in my studies or research?

Griffith's hint can be used as a supplemental tool for solving problems or gaining a deeper understanding of electrodynamics. It can also be used as a starting point for further exploration and experimentation in this field.

4. Is Griffith's hint applicable to all levels of understanding in electrodynamics?

Yes, Griffith's hint can be helpful for beginners as well as more advanced students or researchers. It can be applied to a wide range of problems and concepts in electrodynamics.

5. How can I access Griffith's hint if I don't have the book?

Griffith's hint may be available online through various resources or forums. Additionally, there are other textbooks and study materials that may provide similar hints or tips for understanding electrodynamics.

Similar threads

Surface current density-logic and definition contradict
    • Electromagnetism
Replies
8
Views
4K
Maxwell’s equations with varying charge but constant current
    • Electromagnetism
Replies
22
Views
3K
Why Does Zero Divergence of Current Density Imply Zero Charge Density?
    • Electromagnetism
Replies
8
Views
4K
Faraday's Law with Zero Resistance Current Loop
    • Electromagnetism
Replies
2
Views
6K
Engineering Current density calculation in anisotropic ferromagnetic film
    • Engineering and Comp Sci Homework Help
Replies
7
Views
744
I What does the j means in this notation?
    • Classical Physics
Replies
7
Views
1K
Magnetostatics: What if "steady" currents were divergent?
    • Electromagnetism
Replies
6
Views
2K
I Energy Density in E Field: Does it Contribute to Inertial Mass?
    • Special and General Relativity
Replies
16
Views
1K
I Reconciling Lorentz Four-Force Density w/ Spacelike Four-Current (##c = 1##)
    • Special and General Relativity
Replies
10
Views
1K
Finding the conduction current density
    • Introductory Physics Homework Help
Replies
3
Views
1K

Hot Threads

Recent Insights

Back
Top