Notes by Dushyant Kumar
ELECTRICITY
Class X
Electricity
↓
(as a subject)
The branch of physics that studies
electric charge and the effects caused by it.
There are two types of electricity.
1) Static electricity --- the study of charges at rest.
2) Current electricity ---- the study of charges in motion. Or,
A form of energy produced due to the flow of charges (electrons).
Electricity is a form of energy produced by the flow of charges through a conductor. It is a kind of energy that is easy to use and control. It powers our machines, vehicles, TV, bulbs, fans, computers and all other appliances. Modern way of life is fully dependent on electricity.
CHARGE - Like mass, the charge is the fundamental property of matter.
Charge is possessed by fundamental particles of matter: electrons and protons.
Electrons are called negatively charged particles.
Protons are called positively charged particles.
There are two types of charges:
Positive charge
Negative charge
Unlike charges attract each other and like charges repel each other.
In an atom, the number of electrons is equal to the number of protons. So, an atom is electrically neutral.
When an atom or a material gains electrons, it becomes negatively charged. (How?)
When an atom or a material loses electrons, it becomes positively charged. (How?)
There are some combinations of materials that when rubbed against each other, get charged. Like -----
Glass rod -- silk cloth. : When rubbed, glass rod loses electrons and silk gains electrons.
- When two materials are rubbed and thus get charged, there is always the force of attraction between them because opposite charges are developed in them.
Ebonite rod -- wool
When rubbed, ebonite rod gains electrons and so has excess of electrons and becomes -vely charged. On the other hand, wool loses electrons and so has an excess of protons and thus becomes +vely charged.
In case of plastic comb/pen - dry hair
When a plastic comb or pen is rubbed with dry hair, the plastic comb or pen gains electrons and becomes -vely charged. Since dry hair loses electrons, it becomes +vely charged.
Due to the friction between two materials, there is a transfer of electrons and the materials get charged. The charges produced get confined to the materials (in insulators). This is what we call static electricity.
The S.I. unit of charge is coulomb or C. It means charge is measured in coulomb like distance is measured in meters. The charge on an electron or proton is equal in magnitude but both are opposite in nature that’s why we put minus (-) sign to denote the charge on an electron. Charge on ----
1e = -1.6 x 10-19C
1p = 1.6 x 10-19C
Let’s see how big 1 coulomb is i.e. how many electrons there are in 1C.
1.6 x 10-19C = 1e
1.6 x 10-19x 1C = 1e
1C = 1e/(1.6 x 10-19)
1C = (10/16) x 1019 e
1C = 6.25 x 1018e
Thus, 6.25 x 1018 electrons together make up 1C charge.
1 coulomb is the charge possessed by 6.25 x 1018 electrons.
Another definition of 1 coulomb
1C is that much charge which exerts a force of 9 x 10-9 N on an equal charge placed at a distance of 1m from it.
In other words, two 1C charges placed 1m apart from each other exerts a force of 9 x 10-9 N.
But the question is how 1C charge is related to 9 x10-9 N force. For this, we need to learn Coulomb’s law.
COULOMB’S LAW
Statement: The force between any two charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
On combining the two equations,
Where, F = electrostatic force
K = electrostatic constant
K = 9 x 109 Nm2/C2
(for vacuum or free space)
Now, if we take q1 = 1C , q2=1C and r = 1m
then, F = 9 x 109 N , you can see this is a much stronger force.
ELECTRIC CURRENT
The flow of electric charge is known as electric current.
Electric current is carried by free electrons present in a conductor.
It is represented by the letter ‘I’.
The rate of flow of electric charges is called electric current.
Or,
Electric current is the quantity of charge flowing per unit time through a conductor.
Let’s say, in time t s, Q amount of charge is flowing through a conductor.
The amount of charge flowing per unit time is called electric current I.
Thus,
From the above formula of electric current, the unit of current is C/s. C/s is what is called ampere.
The S.I. unit of electric current is ampere represented by the letter A.
If we take I = 1A
Q = 1C
t = 1s , and put the values in the formula
1A = 1C/ 1s
1 A is the current when 1 C of charge is flowing through a conductor every 1 second.
1C = 1A x 1s
When 1A of current is passing every 1s through a conductor, the amount of charge is 1C i.e. 6.25 x 1018 electrons are passing every second.
Ammeter is the instrument used to measure electric current in a circuit.
Thank You!
