magnetic field

This is the same as in gravitational field (G-field), when in an electromagnetic field (EM field, since electric and magnetic are the two faces of a coin), if you have a charge/ magnet, you will feel a force acting on that charge/ magnet. This is the same force as you used in left hand and right hand rules (in advance level, you will not use left hand and right hand rules). Since in the wire, there are many charges,they will feel the EM field and have a force on them (EM force).

In the case of G-field if you have a mass in the gravitational field, you will feel the gravitational force. They are the same.

2008-11-07 15:55:47 補充：
There is energy in the field, but field itself is not the energy.

2008-11-07 15:57:02 補充：
The field is simply represent the force per unit charge / mass act on the unit charge / mass.

2008-11-07 15:58:53 補充：
When you are in the field, you can feel a force, but if you don't travel in the field, or have a change in the potential of the field, there will be no energy change (gain / loss).

2008-11-07 16:01:19 補充：
An example is the circular motion of satellite in Earth's orbit.

2008-11-07 16:01:59 補充：
It is performing circular motion, the gravitational force used in circular motion.

2008-11-07 16:02:59 補充：
But it does not change in potential, no energy is release/gain from the field.

2008-11-07 16:03:58 補充：
Since there is no monopole for magnet, this is hard to draw a similar example in magnetic field only.

2008-11-07 16:06:35 補充：
By the way, energy is a conservative quantity (same as momentum), if you ask me what is energy (or momentum), I would say in fact I don't know........................

Field, graviational or electromagnetic, is not a force. Field represents a form of energy in space.

A magnetic field would give rise to a force if a magnetic pole is situation in it. This force will do work on the magnetic pole and energy is released from the field onto the pole.

Similar situation happens in other fields. A graviational field gives rise to a force on a mass and would do work on the mass by releasing energy from the field.