Electricity - Class 10th Science
Introduction
Today electricity became one of the most important needs for human. It appears that without electricity we cannot live.
Electricity is a type of energy that can be controlled and used to make our life comfort.
Flow of water through a water body, such as river, ocean etc. is called water current. Flow of wind is called wind current. Similar to that electric charge flows through a conductor and this flow of electric charge is called electrci current.
Substances which allow the flow of electric charge through them are called conductor. Metals are good conductor of electricity. This means metals allow flow of electric charge through them. That's why electric wires are made of metals.
According to some Egyptian Texts of about 2750 BC back, people were aware about electric current. People know about a type of fish which gave shock. Such fish were called 'THUNDER OF NILE' and were considered as protector of fish.
From ancient time it was known that when a rod of amber is rubbed with cat's fur, the rod of amber gets a capacity to attract smaller objects, such as hair, bits of paper, etc. Around 600 BC, Thales of Miletos concluded that friction makes amber magnetic, i.e. it becomes able to attract small objects.
In 1600 BC William Gilbert studied about electricity and gave a new Latin word ELECTRICUS. He got this word ELECTRICUS from from AMBER. In Greek the word ELEKTRON was used for Amber. From this electricus, the English word ELECTRIC or ELECTRICITY came in existence.
Electric Charge
When a glass rod is rubbed with silk, flannel or cat's fur, it starts attracting bits of paper or hair. This happens because glass rod gets charged due to rubbing with flannel.
Similarly, when one combs his dry hair, comb gets a property because of which comb starts attracting bits of paper.
This happens because while rubbing some of the electrons from silk cloth or flannel or cat's fur, are transferred to the glass rod and because of loss of electrons, glass rod becomes positively charged. On the other hand because of gains of more electrons silk cloth gets negatively charged.
Same situation happens in the case of comb when rubbed against dry hair.
A charged balloon can even attract a small empty can towards it.
Positively and Negatively charged bodies
Two positively charged bodied repel each other while two oppositely charged bodies attract each other. Similarly, two negatively charged bodied repel each other and one negatively charged body and one positively charged body attract each other.
Electric charge and Modern View
All matters are composed of atom. An atom composed of electron, proton and neutron. Electrons are negatively charged while protons are positively charged. In all of the atoms number of electrons is equal to number of protons. This makes an atom electrically neutral.
But, when the number of electrons becomes more than that of number of protons, the atom becomes negatively charged. And when number of protons become more than that of number of electrons, an atom becomes positively charged.
The negatively charged or positively charged atom is called ion.
Attraction and Repulsion between ions
Two positively charged or negatively charged bodies repel each other when they come closer, while two oppositely charged bodies attract each other.
Unit of Charge
SI unit of charge is coulomb.
Charge over a proton
A proton has 1.6 x 10 –19 coulomb of charge.
Charge over an electron
A electron has – 1.6 x 10 –19 coulomb of charge.
Charge over a neutron
A neutron is neutral. This means a neutron has no charge.
Electric Current
Water current is flow of water in river or ocean, wind current is flow of wind. Similar to that, electricity flows in conductor, such as electric wires.
In other words flow of electricity is the flow of electric current. Electricity is nothing but flow of charge through a conductor.
Thus, electric current can be defined as "The Flow of electric charge through a conductor is called electric current".
Electric current is nothing but flow of electrons. In other words flow of electrons through a conductor is called electric current.
Direction of Flow of Electric Current
Since, electrons were not known at the time when phenomenon of electricity first observed, thus electric current was considered to be the flow of electric charges. And the direction of flow of positive charges was taken to be the direction of electric current.
Conventionally, in an electric circuit direction of electric current is taken as opposite to the direction of flow of electrons.
This means direction of electric current is taken as in opposite direction of flow of electrons.
How to Express Electric Current?
Electric current is expressed by amount of electric charge flowing through a particular area in unit time.
In other words, electric current is the rate of flow of electric charges.
If a net charge Q flows through any cross-section of a conductor in time t, then the current I, through the cross section is
Where, Ι = electric current
Q = net charge
t = time
Thus, amount of electric charge (Q) flowing through a particular area in unit time (t) is called ELECTRIC CURRENT (Ι).
SI Unit of Electric Current (Ι)
The SI unit of electric current is ampere (A).
This name of SI unit of electric charge is named after the French scientist Andre Marie Ampere.
1 ampere (A) of electric current is the flow of 1 coulomb of electric charge per second.
This means, 1A = 1 C/s
Small quantities of electric charge is expressed in milliampere (mA) or in microampere (μA).
1 mA (milliampere) = 10 – 3 A (Ampere)
1 μA (microampere) = 10 – 6 A (Ampere)
Ammeter
Ammeter is an instrument which is used to measure electric current in a circuit. Ammeter is connected in series in an electric circuit.