You must have seen that if we rubbed any plastic pen with our hairs then it start attracting some small pieces of paper. And you guys must have performed this too. But have you ever wondered why this happens, after rubbing a pen, it starts to pull small pieces of paper.
Not only a plastic pen even a glass rod can also attract small pieces of paper if it rubbed by the silk clothes.
Whenever a glass rod is rubbed with silk, it acquires a power to attract light bodies such as small pieces of paper. But the question is, who gave the rod this attracting power? The agency who gave this attracting power to rod is said to be electrified or charges.
If electricity is generated by the friction then this electricity is called frictional electricity.
In this section we are going to learn about the charges and its basic properties in detail.
Electric Charge has no fixed definition, different physicist gave different definitions time to time.
According to William Gilbert – A charge is something which is possessed by material objects that makes it possible to exert electrical force on the other charged particles.
Some physicist says that – charge is the property (acquired or natural) of the material body due to which it produces and experiences electrical and magnetic force.
Some of the naturally charged particles are electron, proton, α particles etc.
TYPES OF CHARGES
Basically charges are categorised into two categories.
It is the deficiency of the electron compared to protons. Let’s consider a atom having 10 electrons and by any means 3 electrons get escaped from the atom then now this atom has 7 electrons and 10 protons, due to escaping three electrons from the atom protons become dominant over electron by three. So this atom become +3 positive charged.
It is the access of the electron in any system. Let’s consider a atom having 10 electrons and by any means this atom gains 3 more electrons from any other atom. Now in this atom number of electrons is dominating over protons. So atom become -3 negative charged.
UNITS OF CHARGES
Charge is a derived physical quantity. It is measured in coulomb (C) in SI unit. In practice we uses various units such as mC (10^-3 C)
μC (10^-6 C) and nC (10^-9 C) etc.
CGS unit of charge = electrostatic unit = esu
1 coulomb of charge = 3×10^9 esu
Dimensional formula of charge is -[M^0L^0T^1I^1]
Specific charge is defined as the ratio of the charge to its mass.
If anyone wants to find the specific charge then he has to find the ratio of the charge to its mass.
Specific charge = charge / mass
PROPERTIES OF THE CHARGE
Now let’s understand about the characteristics properties of the charge, all the properties of the charge is listed below –
1). Charge is a scalar quantity – charge is a scalar quantity because it adds up algebraically and always represent the the deficiency and acces of electrons.
2). Charge is transferable – Yes, charge is transferable when you charge your phone then the charges is transferred from the electrical source to your phone. Charging implies transfer of electrons or charges from one body to another body.
Positively charged body means loss of electrons i.e dificiency of electrons . And negatively charged body means acces of electrons i.e gain of electrons.
Then we can conclude that mass of negatively charged body is greater than the mass of positively charged body.
3). Charge is conserved – In isolated system the sum of total charges i.e sum of positive an negative charges remains constant, whatever changes took place in that system.
Charge can’t be created nor be destroyed.
4). Charge is quantized – we know that everything is made up of atoms and every atoms is made up of three sub atomic particles i.e electron, proton and neutron.
Let’s consider a body having 100 electrons then what is total negative charge on the body? The total negative charge on the body is given by –
q = 100×1.6^-19 C = 1.6×10^-17 C.
But again take a body having n electrons then what is the total negative charge on it. The total negative charge on the body is given by electronic charge × no. of electrons. So we can say –
The charge on the body is always exist in integral multiple of fundamental unit of electric Charge. i.e Q = ±ne. Where 1e = 1.6×10^-19C
and n is any integer. Millikan’s oil drop experiment proved the quantization of charge.
5). Like point charges repel each other but unlike point charges attract each other.
6). A charged body may attract a neutral body or a oppositely charged body but it always repel the similarly charged body.
7). Charge is always associated with mass, i.e charge can’t exist without mass, mass is necessary for existence of Charge but mass can exist without charge.
8). Charge is relativistically invariant – charge is independent of frame of reference i.e charge on the body did not depend on the velocity. whatever be the velocity charge remains constant. Velocity cannot affect the charge on the body. But mass is variant, the mass of the body depend upon the velocity and it increases if velocity increases.
9). A stationary charge produce electric field around it. But if charge is moving in uniform motion then it produces electric as well as magnetic field. But if it is moving in accelerated motion then it produces electromagnetic radiation in addition of producing of electric and magnetic field.
10). Sum of all the charges in this universe is zero. Existence of negative charge is just for the cancellation of positive charge. If positive charge created then negative charge created automatically and vice versa.
You can watch this video for more reference.