I really want to know that how does battery create a potential difference across the circuit. When we cross the battery from its negative terminal to positive terminal the potential rises by the voltage mentioned on the battery . So what exactly happens between the terminals so that the potential rises ?I know that the chemical energy of battery makes it possible for charge to flow across the battery from low potential to high potential .But i want to know how is potential difference created by battery across the circuit .
This is dealt with in the field of electrochemistry. Here is a simplified explanation:
Chemical reactions involve the outermost electrons of the reactant atoms and some of those reactions can be modeled as one atom "giving" an electron to another.
There are certain types of such chemical reactions in which the electron can be captured and diverted out of the reaction site with conductive wires, used to perform work as a flow of electrical current, and then returned to the reaction site through another wire to complete the reaction taking place there.
An apparatus designed to generate a flow of electrical current captured from a chemical reaction is called an electrochemical cell. The amount of "kick" given to the electrons by the reaction is measured by the voltage difference between the terminal in the cell which extracts the current and the terminal which returns the current. These cell potentials vary from a fraction of a volt to a volt or two.
By stacking a number of cells in series, their voltages add together and an array of stacked cells is called a battery.
On top of the enlightening question already given above, let me state how I imagined the fact that electrons are held in one place (at the negative pole). The electrons are pushed through a one-way exit, of which the door opens only in one direction (to the outside). If they are out they can't get back in anymore. If there is a certain amount of electrons outside (at the minus pole) the door can't be opened anymore. The opposite holds for the plus pole (electrons going in, from the plus pole). The exact mechanism which throws the electrons out (or pulls them in) remains to be seen.