# Electromagnetism, flux density Vs. field size

1. Jan 3, 2010

### semiotically

With a set coil if you increase the electric flow does the flux density increase
And/or the magentic field decrease/ maintain/ increase in size..?

Thanks once again,

Sem.

2. Jan 3, 2010

### DukeofDuke

You mean the magnetic flux through the middle of the coil (called a solenoid)? Yes, it increases if you increase the electric current through wire.

A lot of times the easiest way to see "what happens" is to take a process to a ridiculous proportion. For example, "what happens to magnetic flux if you decrease the electric field of a solenoid" can be answered by the question "what happens to the flux if you decrease the field all the way to 0, that is, turn off the electric field. Obviously the magnetic flux disappears. So yes, making your electric field get closer to 0 makes your magnetic flux get closer to 0 (this doesn't actually logically follow and a mathematician would want proof that the function relating the field to the flux is monotone increasing/decreasing and continuous for example but its good enough for some intuitive stuff).

So yeah, increasing the current increases the flux.

3. Jan 3, 2010

### semiotically

And how does this affect the field size?
Thanks

4. Jan 3, 2010

### DukeofDuke

which field, magnetic or electric?
The magnetic field goes up if the magnetic flux goes up...pretty much by definition
the electric field is present in the wire itself, and also goes up if the current goes up, again pretty trivially...

5. Jan 4, 2010

### Arantheo

I think the ideia is related to a natural tendency that systems show to couterbalence disturbances from equilibrium

6. Jan 4, 2010

### semiotically

HI everyone,

------------

Regarding Q2, when you have a coil without a soft magnetic material
(ferrite, steel, iron, etc) inside, the generated flux density B (or
magnetizing field H) is proportional to the current through the coil's
winding.

For coils with magnetic material, the core material can support a
limited flux density only (300...500 mT for ferrite, and 1.5..2T for
iron/steel). Up to the saturation point, the flux density is more or
less proportional to current to the winding. Above the saturation
level, the field does increase very slowly with increasing current.

---------------

Though I still need any help on frequency-weighting and 'flat' gauss meters..?