One question regarding magnetism/electricity

[shanktank]

hey,
can anyone tell me what the sources of electric fields, magnetic fields, and gravitational fields are? i can't find it anywhere in my textbook.
Thanks a bunch in advance.
Shane

 

[ovoleg]

Sources of Magnetic Field
((Stolen from for time saving purposes http://theory.uwinnipeg.ca/physics/mag/node6.html) )

When we introduced the electric field it was apparent that electric charges were the source of such a field. Experiments in the 19th century showed that the source of a magnetic field was a moving charge, or current. A detailed mathematical relation between a charge moving at velocity and the associated magnetic field is known as Ampère's law or, in another form, the Biot-Savart law.

Electric Field((Stolen from for time saving purposes Wikipedia))
In physics, an electric field or E-field is an effect produced by an electric charge (or a time-varying magnetic field) that exerts a force on charged objects in the field. The SI units of the electric field are Newtons per coulomb or volts per meter (both are equivalent). Electric fields contain electrical energy with energy density proportional to the square of the field intensity. Electric fields exist around all charges; the direction of field lines at a point is defined by the direction of the electric force exerted on a positive test charge placed at that point. The strength of the field is defined by the ratio of the electric force on a charge at a point to the magnitude of the charge placed at that point. In the dynamic case the electric field is accompanied by a magnetic field, by a flow of energy, and by real photons.

Not sure about your question about gravitational fields. Gravity is the tendency of objects to accelerate toward each other(which applies to all objects but only the massive ones have a field large enough to field).

Newtons law of Universal gravitation(wikipedia...lol)