1. ELECTRIC CURRENT.

2. What is electric current ? Electric current is caused due to the flow or movement of electric charges. The flow of electric charges or electrons produce electric current. Electrons :are the negatively charged particle present in atom. The electrons in an atom are arranged in the outer space around the central nucleus.

3. ELECTRIC CURRENT Conducting wire in an electric circuit is made of metal. If we supply it with a source of energy and a complete circuit, then the electrons will all move in the same general direction through the wire. This movement of electrons through a conductor cause electric current. In an electric cell electric current always flow from its positive terminal to negative terminal.

4. WHAT IS AN ELECTRIC CELL? Electrical cells are the source of energy for the electric circuit. Inside the cell are a number of chemicals. These chemicals store energy. When a cell is attached to electric device, the chemicals react with each other. As a result, electrons are given the energy they need to start moving through the circuit- electrons start flowing. The electric current is caused due to the flow of electrons through the conducting wires.

5. CELL

7. ELECTRIC BATTERY Batteries are electrochemical devices that convert chemical energy into electrical energy. Their major components include an anode and a cathode that are separated by a non-conductive separator that will allow the flow of ions but not the flow of electrons, a case and an electrolyte (Figure 1). In battery terminology, the cathode is the electrode through which the electrons enter a cell and the anode is the electrode through which they leave the cell. When the battery is discharged, electrons move from the anode to the cathode as ions move from the cathode to the anode.

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9. Primary batteries Primary batteries - In primary batteries, the chemical energy of chemicals used is changed when the current is allowed to flow and this type cannot be recharged because the chemical reactions are irreversible. Ex. Dry cell Mercury cell

10. Secondary cell These batteries provide electric current as a result of reversible chemical reaction(which are reversed as the cell discharges). Such batteries can be recharged hundreds of times. ex. Nickel-Cadmium (Ni-Cd) Nickel-Metal Hydride (Ni-MH) Lithium ion (Li-ion)- These are used in mobiles,laptops cameras etc.

11. Batteries Primary batteries 1.Lower initial cost 2.Disposable. 3.Typically lighter and smaller; thus traditionally more suited for portable applications. 4.limited to specific applications Secondary batteries 1.Higher initial cost. 2.Regular maintenance required. 3.Traditionally less suited for portable applications, although recent advances in Lithium battery technology have lead to the development of smaller/lighter secondary batteries. 4.Can be used a large spectrum of applications.

12. Photovoltaic Cells The solar cells that you see on calculators and satellites are also called photovoltaic (PV) cells, which as the name implies (photo meaning "light" and voltaic meaning "electricity), convert sunlight directly into electricity. Photovoltaic cells are made of special materials called semiconductors such as silicon, which is currently used most commonly. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely.

13. . PV cells have some arrangement that force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off for external use, say, to power a calculator.