Solenoid field lines

[Njguy]

Everyone here knows how the standard cylindrical solenoid works. This image...
**broken link removed**

depicts the field lines. Obviously the field in the center of the solenoid is vastly more concentrated than the field on the outside of the windings which are more or less shooting out into space (so to speak). My question is, is the entire generated field(electromagnetic energy) on the outside of the solenoid equivalent to the field on the inside and just less concentrated, or is it actually weaker? If the first option is true, it is sad that it cannot somehow be harnessed to do work. A cylindrical coil as depicted in the picture (most common) does not seem to be a very efficient type of winding.

 

[ronv]

I think some have a steel housing around the outside of the coil that improves the magnetic path.

 

[Jaguarjoe]

I think you're talking about leakage inductance. In some cases it can be beneficial as in power transformer self limiting. In other instances, such as automobile ignition coils it is undesireable.

 

[crutschow]

The energy of a field line is constant through its complete path. So the energy in the concentrated lines in the center of the solenoid is equal to the energy of the diffuse (spread-out) lines outside the center.

The efficiency of the coil is greatly improved by having a magnet material in both the inside and enclosing the outside of the coil (as is typically of commercial solenoids). Also the coils are actually wound as close together as possible to minimize spacing and leakage flux between windings.

 

[MrAl]

Hello,

In problems like this you can often find simplifications that lead to an understanding without having to deal with the complexities of the original problem.

For example, the first simplification we can make is to assume that instead of a true helix we just have several concentric rings all with the same current level. The second simplification is to look at only one of those rings, which would have a similar type of field. We can then use concepts like this:
https://www.electro-tech-online.com/threads/analog-to-digital-tlc548.591/
to find out the field inside and outside and make judgments about what is happening to the field inside and outside the ring as we move around in space inside and outside of the single ring.

 

[shortbus=]

Njguy, you should down load some of the free magnetic analysis soft ware that is available -

http://www.quickfield.com/free_soft.htm

http://www.femm.info/wiki/Download