Electrical energy stored in solenoid

Click For Summary

Discussion Overview

The discussion revolves around the energy stored in the electric and magnetic fields of a solenoid with a linearly increasing current. Participants explore the implications of Poynting's theorem and the relationship between electric and magnetic fields in this context, questioning the conditions under which energy is stored in each field.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant claims to have demonstrated that the energy stored in the magnetic field equals the energy being pumped in, suggesting that the energy stored in the electric field is zero.
  • Another participant notes that while the final state may lack a magnetic field, there is a nonzero induced magnetic field during the transition from zero to the desired electric field value.
  • A different participant argues that as the current increases, the magnetic field also increases, leading to a changing electric field, and questions why there would be no energy stored in this electric field.
  • One participant posits that electric and magnetic fields are not distinct entities but rather mathematical models for describing interactions, referencing relativity to highlight the interchangeable nature of electric and magnetic fields from different observers' perspectives.

Areas of Agreement / Disagreement

Participants express differing views on the energy storage in electric and magnetic fields, with no consensus reached on the conditions under which energy is stored in each field.

Contextual Notes

The discussion involves complex interactions between electric and magnetic fields, with assumptions about static and dynamic conditions that remain unresolved. The implications of Poynting's theorem and the nature of energy storage in electromagnetic systems are also under consideration.

PhysForumID
Messages
7
Reaction score
0
I have a solenoid which has a current passing through it which increases linearly with time. I have proved that the energy stored in the magnetic field is equal to the energy being pumped in according to the surface integral of the poynting vector. This implies the energy stored in the electric field is zero (according to poynting's theorem which states the energy change for an EM system is the energy pumped into the E and B fields minus the energy flowing out of the surface in the poynting vector).
Why is the energy stored in the electric field zero? My attempt was that in a static situation (constant current I), the energy is entirely in the magnetic field since there is no electric field, so if we take this linear increase in a quasi-static manner, then the energy stored in each quasi-static situation should be equivalent to the same static situation, so it wouldn't make sense if energy was stored in the E-field in one situation but not in the other.
 
Physics news on Phys.org
Although there is no magnetic field in the final state, there is a nonzero induce magnetic field when you increase the electric field from zero to the desired value. I guess if you take into account this fact you will get a reasonable answer.
 
In a solenoid there is always a magnetic field in the core. As you increase current, the magnetic field increases causing a changing electric field in the core too. Why is there no energy stored in this created electric field?
 
Electric and magnetic fields are not separate things. They are just math. models to help us describe the interaction between charges, moving (B field) and stationary (E field).

Remember from relativity that the concepts stationary and moving have no meaning.
One observer's B field is another observer's E field.

In fact, these ideas of B and E hark back to the concept of the aether and are are so unsatisfactory now that they are being slowly replaced by a better model (The vector and scalar potentials)
 

Similar threads

  • · Replies 16 ·
Replies
16
Views
4K
  • · Replies 14 ·
Replies
14
Views
3K
  • · Replies 16 ·
Replies
16
Views
5K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 21 ·
Replies
21
Views
3K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K