ELECTRIC CHARGE
From the study of atomic structure we know that an atom consists of a central part called nucleus and around the nucleus (called extra-nucleus) there are a number of electrons revolving in different paths or orbits. The nucleus consist of protons and neutrons. A proton is a positively charged particle while a neutron has no charge. Therefore, the nucleus of an atom bears a positive charge. An electron is a negatively charged particle having magnitude of negative charge equal to the magnitude of positive charge on a proton. Normally, the number of electrons is equal to the number of protons in an atom. Therefore, an atom is neutral as a whole, the negative charge on electrons cancelling the positive charge on protons. This leads to the conclusion that under ordinary conditions, a body is neutral, i.e. it exhibits no charge. When a body has deficiency or excess of electrons from the normal, it is said to be charged or electrified.

Types of Charge :
There are two types of charges known as positive and negative charges. All objects normally contain equal amount of positive and negative charges and are therefore, electrically neutral. When we comb dry hair, the comb gets charged and can pick small pieces of paper brought near it. When we rub a glass rod with silk cloth or a piece of ebonite rod with woolen material, the charge acquired by a glass rod rubbed with silk is called a positive charge. and that on ebonite rod, is called a negative charge. Glass rod and ebonite rod will attract each other while two glass rods as well as two ebonite rods will repel each other.

Unit of charge     S. I. unit : Coulomb (C)

Properties of charge
(i)    Charge is conserved during any process.
Example : Chemical reaction, nuclear reaction,etc.

(ii)    Charge is quantized: Electric charge always occurs  as some integral multiple of fundamental unit of charge (e).
Example : The amount of charge present on a body depends on the number of electrons given out or taken by the body, then Q = ± ne. Where n = 1, 2 ,3.......   n 2 /3 , 1 /2 or any fraction

(iii)     Charge is always associated with mass.

(iv)     Charge is transferable: If a charged body is put in  contact with an uncharged conducting body, then it becomes charged due to transfer of electrons from one body to another, this process is called conduction.

(v)     Charge resides on the outer surface of a conductor.

(vi)    Similar charges repel each other while opposite charges attract.

(vii)    Repulsion is sure test for electrification of bodies.

(viii)    Electroscope is a device used to confirm the presence  of charge and its nature on a body.

Introduction

• Light in our houses, offices, roads etc. even past sunset
• To operate pumps which in turn have a lot of applications
• Electrical appliances like refrigerator, fans etc.
• Building houses, installing equipment etc.

Current

• Current is the flow of particles in a particular direction. E.g air currents that cause winds or water currents.
• When particles flow in an electric circuit to produce electricity, it is called an electric current.

Electric current

• The flow of electric charges in a circuit is called an electric current. The direction is taken from the positive terminal to the negative terminal of the battery in an external circuit

Electric cell

Features of an Electric Cell:

• It is a small cylindrical structure which helps in operating the devices.
• A small metal cap is placed on one side and a metal disc is present on the other side.
• All cells have two terminals: Positive and Negative.
• The metal cap and metal disc are positive (+) and negative (-) terminals of the electric cell respectively.
• Chemical energy is converted into electrical energy inside a cell. When the chemicals are exhausted, the cell stops working.

We use electric cells to supply the energy needed for electrons to move around an electric circuit. A battery is a group of two or more electric cells that are connected. The electric cell system works to generate electricity.

Power station: Electricity that we use at homes, in our factories, is supplied from a power station.