The continuous flow of electrons is called electricity. It is of two types:
  • Static electricity
  • Current electricity

The electricity in which the electric charges do not flow or remain at rest is called static electricity. The charged produced on the comb, glass rod, etc. are the examples of it. The electricity in which the electric charges flow is called current electricity. Eg: current through the copper wire, etc.

When we rub a comb on our hair, then electrons of the atoms of the hair are transformed to the comb so that comb becomes negatively charged. When this comb is brought near to the pieces of paper, positive charges accumulate at the edge of the paper, as opposite charges attract. Now, comb starts to attract pieces of paper.

Charges are produced through friction between any two dry materials. Whether a body gets positively charged or negatively, it depends upon the nature of the body.

Nylon or acrylic clothes get charged due to friction with the body for the whole day. While taking off these clothes, transfer of charges take place and crackling sound with sparks is produced.

The sources through which electricity can be generated are the sources of electricity. Examples:
  • Cell
  • Dynamo/generator
  • Photo cell, etc.
A cell is a device that converts chemical energy into electrical energy.
A simple cell is a cell having two metallic plates dipped in an acid solution to generate electricity.
Electrodes are the metal rods which are dipped in acid solution in a cell.
An electrolyte is a solution which splits into its constituent ions when electricity is passed.

Electrode with the negative terminal is known as anode whereas electrode with the positive terminal is called cathode.

The two defects of a simple cell are:

  1. Polarization
  2. Local action

During chemical reaction in a cell, hydrogen gas is produced and it accumulates, it is known as polarization.
It can be removed by using depolarizer like manganese dioxide, potassium dichromate, etc.

Zinc plate used in the simple cell is not pure so impurities present in it provides a conducting path for the flow of charge. This makes the zinc wasted. It is called the local action.
It can be removed by using pure zinc or amalgamated zinc rod.

Local action reduces the life of the cell.

The simple cell is not used to produce current for a long time because of the defects like polarization and local action.

A cell which has paste or powder chemicals and converts chemical energy into electrical energy is known as dry cell.
Simple cell Dry cell
It has liquid chemicals filled in a vessel. It has dry chemicals.
Zinc plate is negative terminal and copper plate is positive terminal. Carbon rod is positive and zinc can is negative.

Simple cell has liquid chemicals and it is difficult to carry from one place to another. Dry cell has no solution. So, it is easier to carry it from one place to another and there is no risk of spilling acid from the dry cell. So, dry cell is more useful than simple cell in our daily life.

Cells are widely used in torch-lights, radio, telephone, electric bells, etc.
It is easier to handle as it does not contain liquid solution
  • It is compact
  • It is cheaper than simple cell

MnO2 is used as depolarizer in a dry cell. When the hydrogen gas is produced and accumulated, then MnO2 reacts with the gas and does not let the hydrogen gas to accumulate at a place. i.e. 2MnO2+ H2 → Mn2O3+ H2O

The conducting path of the electricity where cell, wire, switch and load are connected is called an electric circuit. An open circuit is a circuit in which the current is not flowing or switch is off.
A closed circuit is a circuit in which the current flows or switch is on.

The process of arranging two or more than two cells in a circuit is called the combination of cells.
Its types are:

  • Parallel combination
  • Series combination

If the positive terminals of two or more cells are joined together at a point and all the negative terminals are joined at another common point, then this combination is called the parallel combination of cells.
It's one advantage is:

  • It works for a long period of time.

Its one disadvantage is:

  • In parallel combination, whatever be the increase in the number of cells, the brightness of the bulb will not increase.

If the positive terminal of the first cell is connected to the negative terminal of the second cell and the positive terminal of the second cell is connected to the negative terminal of the third cell and so on, then it is known as the series combination of cells.
It's one advantage is:

  • The brightness of the bulb increases with the increase  in number of cells and vice versa

Its one disadvantage is:

  • It works for a short time
Series combination of cells Parallel combination of cells
If the positive terminal of the first cell is connected to the negative terminal of the second cell and the positive terminal of the second cell is connected to the negative terminal of the third cell and so on, then it is known as the series combination of cells. If the positive terminals of two or more cells are joined together at a point and all the negative terminals are joined at another common point, then this combination is called the parallel combination of cells.
The bulb glows with more brightness. The bulb glows with less brightness.
The bulb glows for a shorter time The bulb glows for a longer time.