Class X | Science | Electricity
notes prepared by Subhankar Karmakar
CHARGE:
Charge is a inherent property of a matter.
Types of Electric Charges:
There are two types of electric charges.
1. Positive Charge
2. Negative Charge
POSITIVE CHARGE:
The charge acquired by a glass rod (rubbed with a silk cloth) is called positive charge.
NEGATIVE CHARGE:
The charge acquired by an ebonite rod (rubbed with a wooden clock) is called negative charge
Property of electric charge:
1. Opposite charges or unlike charges attract each other
2. Similar charges or like charges repel each other
The SI unit of electric charge:
The SI unit of electric charge is called Coulomb.
It is denoted by the symbol C.
1 coulomb charge:
1 coulomb charge is that charge which exerts a force of 9 x 10⁹ N force on an equal charge placed at a distance of 1 m from it.
Proton, Electron and their charge:
By convention, it is taken that electrons are negative charges where as protons are positive charges
Magnitude of a proton and an electron charge is equal to 1.6x10⁻¹⁹ C
Number of electrons in 1 coulomb charge:
Suppose we want to to find out how many electrons will make 1 C
Formula:
If q = magnitude of charge
n = number of of electrons
e = charge of an electron
= 1.6 x 10⁻¹⁹ C
then
q = ne
therefore, n = q/e
= 1/1.6 x 10⁻¹⁹
= 6.25 x 10¹⁸
So, 6.25 x 10¹⁸ electrons together make 1 coulomb charge
Conductors:
Those substances through which electricity can flow are called conductors. All the metals are conductors. Therefore, copper, silver, aluminium, gold, iron etc are all good conductors. One non metal graphite are also conductor.
Insulators:
Those substances through which electricity cannot flow are called insulators. All the nonmetals are insulators. Glass, ebonite, rubber, most plastics, paper, drywood, cotton, Mica, bakelite, porcelain and dry air examples of insulators.
Reason behind the flow of electricity through a substance:
Electricity or electric charge can flow through a substance if the substance contains free electron. The electrons which can move from one atom to another atom freely are called free electron.
Therefore, all the conductors contain free electrons where as all the insulators do not contain any free electron.
Free Electron: The electrons which can easily move from atom to atom are called free electron. They are the the carriers of electricity.
Electric potential: (V)
The electric potential or potential at a point in an electric field is defined as the work done in moving a unit positive charge from infinity to that point.
Explanation: suppose you take an unit positive charge and place it very very large distance which is called infinite distance, from that point if you want to bring/ move the charge against an electric field to a point you have to do a work done, that work done will be called electric potential.
Electric potential is denoted by symbol V.
SI unit of electric potential is called volt. Symbol is V.
Definition of 1 volt:
A potential of 1 volt at a point inside an electric field means that 1 Joule of work is done in moving one coulomb of positive charge from infinity to that point.
Electric potential difference or potential difference:
The difference in electric potential between two points is known as potential difference between that two points.
Definition:
The potential difference between two points in an electric circuit is defined as the amount of work ok done in moving a unit charge from one point to the other point.
Formula:
Potential difference = (workdone)/quantity of charge moved
If W = work done
Q = quantity of charge moved
V = potential difference between two points
then, V = W/Q
SI unit of potential difference is also volt (V)
1 Volt potential difference means it needs 1 joule of work to move 1 coulomb electric charge from one point to the other.
1 volt = 1 joule / 1 coulomb
1 V = 1 J/C = 1 JC⁻¹
Voltmeter:
The instrument by which electric potential difference can be measured is called voltmeter. Voltmeter has high resistance, and it allows only very small current through it. Potential difference is also known by voltage.
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