I Several questions about electromagnetism

Hey, i have several questions about electromagnetism, i hope you will be able to solve these haha :

1) how to define the electric field? i mean without saying E = F/q because a field causes the electric force and not the reverse so we can't use the force yet right?
2) how to snap a capacitor?
3) in an electrical circuit, where is the charge constant in 2 places? Where does this vary? Where is the potential constant? Where does it vary?
4) how does a capacitor work (simply) ? and how to bring the charge to it? Have we to keep continuallu a force to keep the charge in it?

Thks
 
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how to define the electric field? i mean without saying E = F/q
If you start with the conservation of charge then that leads to the existence of a potential, and then the field can be defined simply as the negative gradient of that potential. No forces needed, but the math is more advanced. See here for details:

 

olgerm

Gold Member
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how does a capacitor work (simply) ? and how to bring the charge to it? Have we to keep continuallu a force to keep the charge in it?
if you connect capacitor to a battery, then one of its plates gets charge U*C and another gets charge -U*C . if you disconnect the battery, it remains charged.
 
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jbriggs444

Science Advisor
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3) in an electrical circuit, where is the charge constant in 2 places? Where does this vary? Where is the potential constant? Where does it vary?
In an electrical circuit, one does not normally expect to find any charge build up anywhere. It is one of the rules of circuit theory: The net flow of charge into or out of any device is zero. The net flow of charge into or out of any connection point is zero.

This remains true, even in the case of capacitors. No net positive or negative charge builds up on a capacitor. Instead, positive charge builds up on one side and an equal amount of negative charge on the other so that the total for the capacitor remains zero at all times.

This does not vary. It is one of Kirchoff's laws.

Potentials are normally of no particular interest. Only potential differences are physically meaningful. In an ideal circuit, if a ground point is specified for the circuit, the potential is zero there, by definition. An ideal circuit may often include ideal power sources with a fixed potential difference. The potential difference across such an ideal circuit element is fixed by definition. An ideal circuit will almost always include ideal wires assumed to have zero (or negligible) resistance. The potential difference across the length of an ideal wire is zero (or negligibly different from zero) by definition.

In a real circuit, a ground is often physically realized as, for instance, a big cable attached to a rod driven into the ground. We normally assume that the ground has an infinite capacity to sink current, that it is at the same potential everywhere and that the grounding cable has negligible resistance. For real circuits, these assumptions can sometimes be incorrect.
 

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