Electric fields in Matter

  • #1

Main Question or Discussion Point

Hi,
Suppose we have a polarized object, and wish to calculate D(r) using
D(r) = epsilon E + P

Do we have to account for the electric field that the polarized object creates, or is it enough to just use the electric field which created the polarization?
Thanks

Ray
 

Answers and Replies

  • #2
Meir Achuz
Science Advisor
Homework Helper
Gold Member
2,169
63
That equation relates the total E field to the total D field, so you should include the field due to the object.
 
  • #3
1,679
3
rayveldkamp said:
Hi,
Suppose we have a polarized object, and wish to calculate D(r) using
D(r) = epsilon E + P

Do we have to account for the electric field that the polarized object creates, or is it enough to just use the electric field which created the polarization?
Thanks

Ray

Your question is a touch confusing, and the equation is incorrect.

The correct equations which both apply to your question are:

[tex] D = \epsilon E [/tex] and
[tex] D = \epsilon_0 E + P [/tex]

In the first equation, the E is the actual E in the material but the epsilon
is related to the material, not to free space. In the second equation, the
epsilon is the epsilon of free space but the E is not the E which you would
measure in the material.

The object will have a different electric field inside it than the electric
field which would have been present if the object were not there.
The D vector does not change whether the mateiral is there or not.
 
  • #4
Meir Achuz
Science Advisor
Homework Helper
Gold Member
2,169
63
I assumed that Ray did leave the subscript 0 out of the epsilon.
The E is the same in each of Antiphon's trwo equatiopns.
The equations are just related by the connection between epsilon and chi, the electric susceptibillity.
 
  • #5
Hi,
Thanks for the replys, it turned out i only needed to include the field that created the polarization. Help was appreciated.
Thanks

Ray
 
  • #6
1,679
3
Meir is right. It's the same E in both equations.
 

Related Threads for: Electric fields in Matter

Replies
1
Views
2K
Replies
5
Views
2K
Replies
1
Views
1K
Replies
9
Views
594
Replies
23
Views
962
  • Last Post
Replies
8
Views
3K
  • Last Post
Replies
2
Views
619
Replies
8
Views
2K
Top