By Nitin Oke For Safe Hands Akola www.safehandsakola.org Electric current By Nitin Oke For Safe Hands Akola www.safehandsakola.org

Charge Similar to magnetism it was found by accident that when amber rod is rubbed by silk cloth it develops ability to attract substances irrespective of whether they are magnetic or not. Latter on this property was called as “static electricity” Like charges repel and unlike will attract.

Information about charge Charges are either positive or negative. Charge is measured in coulomb represented by “C” Charge on electron is -1.6 x 10-19C. When electrons move from one place to other in one direction then it is called as “current electricity” To make the charge flow there is a cause by name “electromotive force” The electromotive force is measured in “volt” (V) The device which produce this electro motive force is called as “cell”

Source of emf The “cell” can be created by Converting chemical energy into electro motive force is called electrochemical cell Converting solar energy into electro motive force is called solar cell Converting mechanical energy into electro motive force is called “dynamo” Please note that flow of electrons is in opposite direction of conventional current.

Cells Basic chemical cell is “Volta’s cell” it consist of two plates (called as electrodes) one made of Zinc (act as negative terminal) and copper (act as positive terminal. Bothe are immerged in “electrolyte” which is dilute sulphuric acid (H2SO4) Green dot represents electron and red arrow indicate conventional arrow. Cu Zn

Leclanche cell This cell consist of zinc rod as negative electrode. Carbon rod act as positive electrode and mixture of manganese dioxide and carbon along with ammonium chloride act as electrolyte. This cell was designed by Georges Leclanche of France.

Dry cell Dry cell is an example of primary cell For Safe Hands By Nitin Oke Dry cell is an example of primary cell This cell consist of a carbon rod acting as positive terminal of cell. Zink cylinder act as case as well as negative terminal. Moist paste is filled between the gap of rod and case. The assembly is sealed by “Lac” sealing wax.

Structure of Dry cell Metal cap Paper or foil cover Pitch seal For Safe Hands By Nitin Oke Metal cap Paper or foil cover Pitch seal Zinc Case and negative terminal Carbon rod and positive terminal Powder of MnO2, ZnCl2 and carbon Paste of Ammonium chloride Negative terminal

Secondary cell The cells used in cars or emergency lights or inverters are secondary cells. Electricity is not generated by this cell, the electrical energy obtained from an external source is stored in it. The cell consist of lead plate and lead oxide plate immerged in sulphuric acid. While charging the lead plate is connected to negative terminal and lead oxide to positive terminal. When external source is disconnected the lead plate becomes positive and lead oxide serves as negative.

Secondary cell Another common rechargeable cell is Nickel cadmium cell. In this cell metal cadmium act as negative pole and nickel as positive pole. The alkali potassium hydroxide is filled in to act as electrolyte.

Note the following If the positive and negative terminals are changing then such source is called as “alternating source” and current due to such source as “alternating current ”(AC). At home we have AC supply and is of 230V It alters 50 times in a second means frequency is 50Hz, The maximum current we get is of 5A The dry cell provides 1.5V Battery used in vehicles is ranging from 8V to 60V Substances can be classified as conductors, semiconductors and insulators.