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For the first one: I would say, for electric current you need electric charges (electrons) to move in a particular direction, so we need to put FORCE on them, how to put force on charges? create electric field.. how to create electric field?! have two big plates one positively charged and one negatively charged... that's the idea of a battery
For the third one: An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery (or "voltaic pile") in 1800 by Alessandro Volta, batteries have become a common power source for many household and industrial applications. There are two types of batteries: primary batteries (disposable batteries), which are designed to be used once and discarded, and secondary batteries (rechargeable batteries), which are designed to be recharged and used multiple times. All batteries contain one or more cells, but people often use the terms battery and cell interchangeably. A cell is just the working chemical unit inside a battery; one battery can contain any number of cells. A cell has three main parts: a positive electrode (terminal), a negative electrode, and a liquid or solid separating them called the electrolyte. When a battery is connected to an electric circuit, a chemical reaction takes place in the electrolyte causing ions (in this case, atoms with a positive electrical charge) to flow through it one way, with electrons (particles with a negative charge) flowing through the outer circuit in the other direction. This movement of electric charge makes an electric current flow through the cell and through the circuit it is connected to. WORKING OF A BATTERY: The potential or voltage difference created between two metals which are immersed in an electrolyte (acid), is called 'cell voltage'. A battery converts chemical energy of the metals submerged in electrolyte into electrical energy by means of an electrochemical oxidation-reduction process. http://en.wikipedia.org/wiki/Battery_(electricity) http://www.explainthatstuff.com/batteries.html http://www.indiacar.com/infobank/batterymaintain_od.htm
The second one is just that you have to say what is power? Power is the ability to take control over something wether it be over power or over a person or even over an item. I think you can do the rest! Hope this helped!