How current actually works?

1. why when we connect the cell, the will be a electrical potential difference formed? How it forms?

The potential difference across the +ve and -ve terminals of a cell is always there. Its existance is because of the chemical reaction occurs between the electrolyte and the materials of the +ve and -ve poles. The chemical reaction forces electrons leaving the +ve pole (hence it becomes positively charged) and attaching to the -ve pole.

2.Why the number free electron in conductor is greater than insulator? What porperties affect the number of free electrons?

Conductors are mostly metals. Atoms of metals generally have one or two electrons in their outer-most electon shell. Since these outer-most electrons have been shielded off by those electrons in inner orbits from the +ve charged nucleus , they experience much less attractive force. As such, these electrons are easily detached from the atoms and become "free-electrons", i.e. they are free to move.

Atoms in insulators generaly forming stable covalent bonds with neighbouring atoms. The orbital electrons are not easily detached from their obits to become free-electrons.


3.How reistance form and why it is formed? How does it affect the spped of electrons that passing through it?

Resistance is an inherent property of a substance. When free electrons move under the action of an electric field in a conductor, they collide with the atoms of the conductor. Such collision process slows down the speed of the moving electrons. This slowing down of electron speed is observed as "resistance to current flow".

Roughly speaking, the higher the resistance of a substance, the lower is the mean speed of free electrons passing throuht it. It is simply because higher resistance indicates there are more collisions between atoms and the free-moving electrons, hence lowering the electron speed.

I'm not sure answer in English is good to make you understand, but attached a "Chinese" explaination of simple zinc-carbon battery/alkaline battery "chemical reaction" which show you where the electrons comes from and why they flow.


Basically the answer to all of you questions is "material" properties:
1. It is all about materials properties in which metal poles of the battery acts as the conductor for the electrolyte (liquid/semi-liquid) materials to release the electrons. The chemical level of the electro-potential determines the "voltage".

2. Different electrolytes have different free electron and different metal poles create different electro-potential (to accept electrons). Insulator, by its material property, does no have any free electron in the molecular, or does not easily react to other molecules with a chemical potential/electron charge.

3. Resistence is also a "meterial" property of its conduction of electrons through its molecule. For example, metal molecule will conduct electron if one end has higher electro-potential than the other end, so it is like the electron travel through it easily (in molecular level it is the molecule shifting its own electron to the next molecul). Non-metal or in the case of battery may be just "paper" as insulator, does not have any "elecron" to pass/shift to the next molecule, so the "resistence" is high.