Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

I need a full explantation for this concept.

Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid.

share|improve this question
    
Why do you think so? A straight solenoid is clearly a limit of a very large thin torus, so if it were possible for any torus, it would be possible in the straight limit, too. If the currents are running strictly around the surface of the solenoid or torus, the field will be inside and strictly vanish outside. –  Luboš Motl Sep 23 '12 at 7:11
    
This is not from my thoughts. I found this piece from a book. But lost it somewhere. –  BigSack Sep 23 '12 at 7:17

1 Answer 1

up vote 4 down vote accepted

This is a solenoid and its magnetic field lines.

solenoid

This is a toroid and its magnetic field lines

toroid

A solenoid by construction has two magnetic poles at the edges when current is flowing through its windings.

One can think of a toroid as a solenoid that has been curved and joined so no poles are open. A toroid can have magnetic fields outside its geometrical boundary according to the way the currents are flowing, if there is a circumferential current that has not been neutralized. Once neutralized there is magnetic field only inside.( as described in the link given above). A neutralizing design is shown below.

neutralizing circumferential current

In contrast a solenoid will always have two open poles.

share|improve this answer
    
Thanks! Have a nice day –  BigSack Sep 23 '12 at 12:49

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.