#Technical Studies – Study 24
Electrical technology is the branch of engineering that deals with the flow of current in conductors. We all know that electricity is very essential for us and we use it for various purposes in our day to day life. As the user of electricity we all have the curiosity to understand the functions and properties of electricity.
In this study you will learn about the basics of electricity.
Electron, proton, neutron, and nucleus:
Each matter is composed of atoms. Atoms are the basic particles of a matter. To understand the basics of electricity you need to understand the theory of atoms.
An atom has four main parts – electron, proton, neutron, and nucleus. Nucleus is present in the centre of atom and has proton and neutron inside it. Outside the nucleus there are electrons revolving around it in different orbits like planets around the sun. Each orbit contains a certain number of electrons which is decided by rule. In this rule ‘n’ stands for number of orbit.
Electrons are negatively charged particles and protons are positively charged particles in an atom. The mass of a proton is 1837 times greater than an electron. There are equal numbers of protons and electrons present in an atom. Therefore an atom is neutral in nature as positive charge of proton is cancelled by the negative charge of electron.
Electric charge and its unit:
Electric charge is the property of matter that defines the number of protons and electrons an atom has. If a body is positively charged, means it has more protons than electrons. Similarly, if a body is negatively charged, means it has more electrons than protons.
SI unit of electric charge is coulomb. The symbol of electric charge is C.
The charge of electron is coulomb.
The electrons in the first orbit of the atom are tightly attached to the nucleus but the electrons in the last orbit are weakly attached to the nucleus. Hence these electrons are called as free electrons. Free electrons can be removed from the atom easily. In fact they move randomly from one atom to another in a material.
According to the presence of free electrons, materials are divided into three categories.
- The materials with large number of free electrons are known as conductors. These materials allow electric current to flow through it easily. Copper, silver, gold are the examples for conductors.
- The materials with few or almost zero number of free electrons are known as insulators. These materials don’t allow electricity to flow through it. Plastic, rubber, paper, ceramics are the examples for insulators.
- The materials whose number of the free electrons is lies in between conductor and insulator are known as semiconductors. These materials are neither conductors nor insulators. Silicon, germanium, carbon are the examples for semiconductors.
Flow of charge in certain direction is known as electric current. When voltage is applied to a conductor the free electrons start to flow towards the positive terminal of the voltage source. The direction of current flow is assumed the opposite direction of flow of free electrons.
Electric current is the rate of change of flow of charge and denoted by the symbol (I).
Current I = =
Therefore the unit of electric current is coulomb/sec or ampere.
Electric potential and voltage:
Electric potential can be defined as the ability of a charged body to do work. It is denoted as V.
Electric potential V =
The unit of electric potential is joules/coulomb or volt.
If we consider two charged bodies with different electric potentials, there will be a difference in potential between those bodies. This difference is called as potential difference or voltage.
If we connect these bodies through a conductor, current will start flowing from highest potential to lowest potential. As the unit of electric potential is volt, the unit of potential difference or voltage is also volt.
Resistance is the opposite force applied to the flow of current by the atoms and molecules of the matter. The current opposed by the resistance is dissipated to the environment in the form of heat. It is denoted as R.
The SI unit of resistance is ohm. The symbol is Ω.
The resistance of a conductor is directly proportional to the length of the conductor.
The resistance of a conductor is inversely proportional to the area of the conductor.
By combining equation (1) and (2) we get
is the constant. It is known as rho. This constant is known as specific resistance or resistivity. The resistivity of a material depends upon its nature.
Therefore the unit of resistivity is ohm – m.
The reciprocal of resistance is known as conductance. It is denoted as G.
The SI unit of conductance is mho. Another unit of conductance is siemen. The symbol is S.
The reciprocal of resistivity is known as conductivity. The symbol of conductivity is σ.
Therefore the unit of conductivity is
Impact of temperature on resistance:
The resistance of material changes with the change in temperature. The impact of temperature is different for different materials.
- The resistance of conductors increase with the increase in temperature. Therefore these types of materials have positive temperature coefficient of resistance.
- The resistance of insulators and semiconductors decrease with the increase in temperature. So these types of materials have negative temperature coefficient of resistance.
- In case of alloys very small increase in resistance occur with the increase of temperature. This increase in resistance is very negligible.
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