# DC doesn't cause electromagnetism?

1. Nov 10, 2009

### PrincePhoenix

DC doesn't cause electromagnetism? That is what our teacher says. Can anyone explain why it doesn't? As far I remember I made an electromagnet from a nail by passing current through it from a battery cell about 6 years ago.

2. Nov 10, 2009

### Born2bwire

Electromagnetics deals with time-varying electromagnetic waves which cannot arise due to DC sources. These are waves composed of oscillating electric and magnetic fields. The limit of electromagnetics when we go to DC is the electrostatic and magnetostatic theories. Magnetostatics certainly provides for a DC current to produce a magnetic field. Perhaps you misunderstood or your teacher mispoke.

3. Nov 10, 2009

### mikeph

Any charge creates an electromagnetic field, let alone current in which the field has both electric and magnetic components.

DC doesn't cause a varying magnetic field, which is required for certain electromagnetic components, eg. transformers.

4. Nov 10, 2009

### nucleus

5. Nov 10, 2009

### ernestpworrel

I think what your teacher meant is that DC running through a straigh piece of wire will not produce a magnetic field although I'm not sure about that either. If you wrap a wire around a nail several times and run DC through the wire you will get a magnetic field though. It has to be an iron nail, no brass or steel.

6. Nov 10, 2009

### Staff: Mentor

7. Nov 10, 2009

### ernestpworrel

8. Nov 10, 2009

### Staff: Mentor

Methinks PrincePhoenix should ask his teacher about that. I'm not very good at mind-reading, especially when I've never even met the person whose mind I'm trying to read.

9. Nov 11, 2009

### PrincePhoenix

He just says that DC doesn't work. And I might be doing something else in my "nail electromagnet" that I don't understand.

10. Nov 11, 2009

### mikelepore

But for what purpose? Your phrase "cause electromagnetism" is unclear.

These are the generalizations about electric charge:

1. Any charged particle, moving or not, just because it exists, causes an electric field.

2. If the charged particle is also moving, including the case of any current in any wire, constant or not, straight or curved, then, in addition to producing an electric field, it also produces a magnetic field.

3. If that current keeps varying, in either magnitude or direction, then it also produces electromagnetic *waves*, which transmit energy.

11. Nov 11, 2009

### Staff: Mentor

No, a constant DC current does produce a magnetic field, period. Besides the Hyperphysics link that I posted, I've also done lab experiments which use an ordinary magnetic compass to study the magnetic field produced by a straight wire that carries a few amps of DC current.

12. Nov 11, 2009