Re: electro-static charge of planets


mainargv@xxxxxxxxx wrote:
Randy Poe wrote:
mainargv@xxxxxxxxx wrote:
alanrockwood2000@xxxxxxxxx wrote:
You asked four questions. Here are some answers to those four, plus a
few extra comments:

1) Yes, at least in principle.
2) Can you clarify what you mean by the second question? There are
several ways one could interpret "electro-static inbalance of planets"

inbalance simply means, when an object has net charge zero, but with
part of it being more negative while the opposite part more positive. I
guess this is possible-- my textbook says a charged object can induce
imbalance in another object, like a charged rod can attract tiny piece
of paper, which is neutral but imbalanced (induced)?

First an inbalance needs to be induced on the paper. For
instance, you rub the paper on something so that the
paper gets one charge and the other object gets an
equal and opposite charge.

A charged rod won't attract a neutral piece of paper.


3) Yes, mostly neutral, mainly because a very small amount of charge
will produce an enormous amount of energy, so even a small amount of
charged material (in terms of moles) would make the system highly
unstable. For example, calculate the electrostatic energy of one mole
of electrons confined to one liter. It would dwarf the energy of an
atomic bomb by many many orders of magnitude.
4) Yes and no. The number of positive charges balances the number of
negative charges to a very good approximation. However, even a small
charge imbalance can produce a very large electric field, and it is
likely that a planet carries at least a small net charge.

the reason I guess earth has an imbalance is simply that earth has a
magnetic moment? so compass works?

Magnetic fields are induced by currents. No charge imbalance
is needed to create current.

For instance, when current is flowing in a metal wire, it is carried
by free electrons which are able to move. However, the
positive iron nuclei are still there, with equal and opposite
positive charges balancing the electrons. Overall the
wire is neutral, but the negative charges are in motion against
the positive background. This creates a current and a
magnetic field.

I guess vaccum is a very good insolator, so if there is any charged
planet around, earth will probably get magnetized (induced imbalance)
and get attracted over...

You seem to be confusing electrostatics and magnetism. There
seem to be several points of confusion in that paragraph.

I know you would need a movement (or was it acceleration?) of a
electric field to induce a magnetic field.

Incorrect. You're still confused about the nature of magnetism
and electricity.

A changing electric field is one thing that can induce
a magnetic field. That is Faraday's Law. The effect is called
magnetic induction.

A current is another thing that creates a magnetic field. That
is Ampere's Law. Different effects, studied by two different
physicists.

But since planets are always moving, it's kind difficult to tell?

No, it is not difficult to tell when you have a current.

Imagine an electromagnet, a coil of wire attached to a current
source. When the current is flowing, you get a magnetic field.
When the current is not, you get no magnetic field. It is not
difficult to tell the difference.

You are doing this experiment on earth. The fact that the earth
is moving has nothing to do with the fact that the current must
be flowing in order to create a magnetic field.

Same thing with the currents flowing at the earth's core. The fact
that the earth moves around the sun has nothing to do with it, nor
does it make it "difficult to tell" if that current is flowing.

Besides, moving probably means
"moving relatively with another EM field"?

No.

Think about the electromagnet experiment I described above.
What does "current flowing" mean? Does it mean "moving relatively
with another EM field"?

Since they (electric,magnetic) always happen at the same time

No.

A bar magnet is a static magnetic field with no associated
electric field.

A charged piece of paper has a static electric field with no
associated magnetic field.

- Randy

.

Relevant Pages

  • Re: electro-static charge of planets
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    (sci.physics.relativity)
  • Re: Redshift without expansion
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