Every material is made up of an atom and every atom is made up of two types of charged particles. They are protons and electrons. Protons are positively charged and electrons are negatively charged. Different metals like copper, iron, aluminium etc consist of a large number of free electrons. When this free electron flows continuously in a certain direction, electric current is produced. Therefore, current electricity is the continuous flow of electrons. Current electricity is a form of energy. It is used for various purpose. It can be easily converted into heat energy, light energy, sound energy, magnetic energy, etc.

Sources of Electricity

Electricity has become one of the important part of human life. It is very difficult to live without electricity. We use various types of electrical appliances such as computer, television, radio, mobile, refrigerator, calculator, watch etc. These appliances make our life easier and comfortable to live. To run all these appliances, we need electrical energy. Electrical energy is also very important to run various industries, factories, transportation systems and many other important things. The devices from which we obtain electricity are called sources of electricity. The three major sources of electricity areas follow,

• Cell
• Photocell or Solar cell
• Dynamo or Generator

Electric Circuit

An electric circuit is a path through which an electron from current source or voltage flows. It is also the path made by connecting a cell, a conducting wire and a bulb. There are various things that are required for making an electric circuit which are discussed below,

• Cell or Battery: It is the source of electricity through which we obtain electricity.
• Conducting wire: It is the path or medium through which electric current flows.
• Bulb: A bulb is a device that produces light and heat energy from the electricity. It is also called a load. It shows the effect of electric current.
• Switch: It is a device used to open or close an electric circuit.

Open circuit and Closed circuit

An open circuit is a type of circuit in which the switch is made 'OFF' and the bulb does not glow. During this condition, the current cannot flow through the wire. So, the load cannot function when the circuit is opened. Talking about the close circuit, it a type of circuit in which the switch is made 'ON'. In a closed circuit, the bulb glows as the current flows through the circuit continuously.

Symbols used in Circuit Diagrams

While drawing circuit diagrams, we cannot draw all the components used in electric circuit. It is very difficult and takes lots of time to draw the various components like battery, wire, voltmeter,galvanometer etc. So, to save time and for easy, various symbols representing various components used in electric circuit are used. Some of the symbols that are used moslty in an electric circuit are given below,

Combination of Cells

Cell is also one of the sources of electricity. It produces electric current. We use cell for various purpose. Sometimes we need low voltage and sometimes we need high voltage. To have different voltage, we should connect the cells in different ways. Mainly there are two ways of combination of the cells which are discussed below,

• Series combination: Series combination is a combination of cell in which the positive terminal of the first cell is connected with negative terminal of the second cell and positive terminal of the second cell with the negative terminal of the third cell and so on. Here, the brightness of the cell increases with the increases in number of cell asthe current increases when the number of cell is increased and decreases with the decrease in number of cellas the current decreases when the number of cell is decreased. It is especially done when more current or voltage is required.
  In series combination, the total voltage is equal to the sum of the voltage of the individual cells. If V be the total voltage and V1, V2, and V3be the individual voltage of cell C1, C2, and C3 respectively, then the total voltage is given by,
  V = V1+ V2 +V3
• Parallel combination: The combination of cells are said to be connected in parallel combination when the positive terminal of all the cells are connected together in one common point and negative terminal of all the cells are connected together in another common point in a circuit is known as parallel combination of the cells. In this combination,the brightness of the light does not increases with increase in number of cells. Here,the bulb glows for longer time than in series combination of the cells. It is especially done when less voltage and high current is required
  In parallel combination, the total voltage of the circuit is equal to the individual voltage of each cells.In series combination, the total voltage is equal to the sum of the voltage of the individual cells. If V be the total voltage and V1, V2, and V3be the individual voltage of cell C1, C2, and C3 respectively, then the total voltage is given by,
  V = V1= V2= V3