# Concept of a Magnetic Field

I was reading a physics book by some author and I got a little too confused with the explanation he stated about magnetic fields.

A magnetic field is a field of force produced by current-carrying conductors or by permanent magnets.

Correct me if I'm wrong: A magnetic field is basically a region / space where magnetic lines / flux lie. Thus, any magnetic objects inside the magnetic field will be attracted or repelled depending on its charges. Thus, this means that if a magnetic object is inside the magnetic field, the object should feel either a pulling or a pushing force acting on it. So, if the current-carrying conductors will produce a magnetic field, then this somehow means that I am inside a magnetic field produced by the current-carrying conductors (microchips and the wires inside the computer). And I believe I have enough metals around the computer, why don't my magnetic metals not experience any force acting on it?

• To add to the answer you have, the definition of 1 Ampere is the current that causes a (magnetic) force of 2e-7N between two parallel, infinitely long conductors of negligible diameter per meter of their length. That's a pretty small force for a not so small current. Having said that, once you go to millions of Ampere of current flowing in small geometries (aka "pinch"), the forces do become truly crushing: en.wikipedia.org/wiki/Pinch_(plasma_physics) – CuriousOne Jun 26 '15 at 18:17

The answer is partly because the currents are very small, so the forces are very small.

Partly electronic devices are carefully shielded to keep electromagnetic fields from getting out. The case plays an important part in this.

Partly the currents are oscillating at a very high frequency. This changes the nature of the effects. Light is an oscillating electromagnetic field.

The frequency of light determines how it interacts with things around it. Light with short wavelengths excites certain receptors in your eye and you see blue. Longer wavelengths excite other receptors and you see red. Longer still and you don't see it at all, but radios can detect it.

Electronics give off radiation at a high enough frequency that they will disturb other electronic devices. Also higher frequencies lead to more radiation than lower frequencies. Thus the need for shielding.

Light exerts very small forces on macroscopic objects like me. But it does exert enough force on an electron in a molecule to kick it into an excited state. This is how receptors in your eye work. They also can make electrons in a conductor move. This is how a radio or a cell phone receives a signal or interference.

A magnetic field is not a region, rather, as the name suggests, it is a field, namely a gauge connection on a chart of a space-time manifold. In other words, it is a map associating a set of numbers to each space-time point: $$\pi\colon(x,t)\mapsto B_j(x,t)$$ whose collection defines the components of the vector $\textbf{B}(x,t)$ according to the projection $\pi$. The explicit form of this map is given by the solution of the Maxwell equations at the point $(x,t)$.

However, as you said, yes, current-carrying conductors will produce a magnetic field and all the metals you have will indeed feel the contribution, in particular so will the initial currents that generated the field in the first place (this is usually referred to as self induction or self interaction).