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Electricity and Circuits
Electricity is a kind a energy. It comes from the charged particles called electrons and protons inside an atom.
We have two types of electricity
a) Static Electricity: It is formed over an insulator and can’t move through it.
b) Current Electricity: Here charges move in a particular direction through a conductor.
Static electricity is also known as frictional electricity. When one object is rubbed by another object, heat so produced, get absorbed by electrons over their surface and they exchange electrons. One of them loses some electrons where the other gain some electrons equally. Both of them gain electric potential. Respectively the first one is called as positively charged object and said to be at positive potential and the second one is called as negatively charged object and is said to be in negative potential. For example when a glass rod is rubbed by fur, the glass rod looses electrons and becomes positivley charge where as the fur gains electrons and becomes negatively charge equally.
The potential of such accumulated charge is defined as the work done in bringing unit positive charge from infinity to the given charge.
A collection of positive charge has a potentoa; of +1V if 1J of work is done in bringing +1C charge from infinite to that given charge.
Here V is potential measured in Volt (V); W is the work done measured in Joule (J) and Q is the charge measured in coulomb (C). 6 × 1018 electron together makes 1 coulomb charge. 1 J work done = 1 m displacement of any thing by applying 1 Newtons force.
Current Electricity: Let us consider a positively charged object and a negatively charged object are connected by conducting wire is shown below:
It is obvious that at B electrons are at high pressure than at A an so electron will start drifting over the conductor from B to A. This fact is called as current of charges or electric current. Current is defined as the rate of flow of charges and expressed as,
I (current)= Q (charge)/ t (time)
It is 1 ampere current if at any cross-section of the conductor 1 coulomb charge passes in 1 second. So, 1A = 1C/1 Sec
Thus electric potential difference can produced electric current. Electric current can be obtained commercially in two ways. One way is from power plants which we shall learn later.
The other way is from a electric cell which is a source of electric potential difference. We shall learn more about cell and shall learn how electric circuits are made by using a cell.
Electricity plays a very important role in our daily life. It lights, heats and cools our homes, and also performs a number of routine jobs for us. Most of the charm of modern life would be missing if there were no electricity. Electricity flows through electric wires. Electricity in motion is called current electricity.
SOURCES OF ELECTRIC CURRENT
a) Small Sources of Electric Current: Cell are small sources of current. In a cell chemical energy changes into electrical energy. A cell basically consists of two terminals — a metal cap on one side and a metal disc on the other. The metal cap is the positive terminal and the metal disc works as a negative
terminal. The chemicals stored in the cell produce electricity.
Cells are of two kinds:
1. Primary Cells 2. Secondary cells or accumulators.
1. Primary Cells: These cells provide current as a result of the chemical reaction that takes place in the chemical reaction that takes place in the chemicals stored in them. When the chemicals are used up, they stop producing electricity. They cannot be recharged. It means the chemical reaction is irreversible. Simple voltaic cell, Leclanche cell, Daniel cell, dry cell, etc., are examples of primary cells. The dry cell was discovered by French scientist G. Leclanche in 1868. It is the most commonly used cell and is used in torches, transistors, calculators, cameras, tape-recorders, etc. This cell is called dry cell because it doesn’t contain any liquid chemical .
A dry cell consists of a zinc casing and a carbon rod with a brass cap at its centre. The carbon rod is surrounded with a black powder which is a mixture of manganese dioxide (MnO2) and graphite (C). This black powder is either contianed in a thin bag of cloth or is surrounded by a thin layer of swadust. The space between the zinc casing and the sawdust is filled with a thick paste of ammonium chloride (NH4Cl).
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