# How can the neutral outer core generate a magnetic field?

• AustinLee

#### AustinLee

Even if the outer core is convecting and conductive it is still charge neutral, so how can a Magnetic field be generated? Maxwells Equation say there needs to be net charge moving for a Magnetic field to be generated.

I assume we're talking about Earth's core?

Even if the outer core is convecting and conductive it is still charge neutral, so how can a Magnetic field be generated?
A current-carrying wire is charge-neutral, nevertheless it generates a magnetic field. Its negative charges (mobile electrons) move, but the equal amount of positive charge (metallic ions) does not.

A current-carrying wire is charge-neutral, nevertheless it generates a magnetic field. Its negative charges (mobile electrons) move, but the equal amount of positive charge (metallic ions) does not.
Okay I can understand the neutrality. However does that mean the Earth's outer core has a electrical current?

Even if the outer core is convecting and conductive it is still charge neutral, so how can a Magnetic field be generated? Maxwells Equation say there needs to be net charge moving for a Magnetic field to be generated.
So let's assume there is a magnetic field (maybe much weaker than the magnetic field of earth) and a neutral conductive liquid is moving in this field. Then there will be some charge separation as the electrons and nuclear charges are deflected in different directions. The amount of charge built up will be limited by the build up of an electric field till some equilibrium is reached. Nevertheless the speed of negative and positive charges may be different thus leading to an additional magnetic field. If oriented parallel to the original field, this can lead to a rapid build up of a strong magentic field starting from a small random field fluctuation.

Wasn't there recent work using a stirred, near-spherical tank of liquid Sodium ?? If the volume was big enough, a bipolar magnetic field spontaneously developed...
I find that astonishing...