Every part of matter is made up of atoms. Atoms are called the building blocks of nature. These atoms consist of a nucleus and shells. The protons and neutrons are part of the nucleus and the electrons are distributed in shells around the nucleus. The protons have a positive charge, neutrons are not charged and the electrons are negatively charged. Electrons have no overall mass while neutrons and protons both have a mass of 1 unit. This is how the relative atomic mass is calculated, by adding up the number of protons and neutrons.
The electrons are distributed in the shell in order of the amount of energy that they hold. So according to that I will introduce the concept of electricity. Electricity is a flow of electrons. Electricity can be transferred by some materials and some cannot transfer it. Conductors are any materials or substances that can allow heat or electricity to pass through them. Conduction means that heat or current is transferred from atom to atom on its way out.
Some materials are good conductors; some are bad conductors while some do not conduct at all.
Such materials or substances that do not allow heat or current to pass through are called insulators. These insulators usually do not have enough electrons to carry the current and thus they are non-conducting substances. One example is plastic. Electrons carry current. In a substance that has many free electrons, current can be carried. Free electrons means that these electrons do not belong to the atom because they are very far from the nucleus and so they can escape easily.
These free electrons make certain substances conductors.
They are either very far from the nucleus or they are electrons that were part of a bond but now are not part of the ionic bond, thus they are in excess. The free electrons are those electrons that are transferred from a positive to a negatively charged ion. This is called the free electron theory. Electricity is basically the transfer of electrons from one atom to the other. In conductors, the atoms are moving in different directions. But when the potential difference is applied between the ends of the conductor, the atoms line up and move to one direction.
Electric conductivity means that a certain substance can carry an electric current. Current is a flow of electrons. So the material that can conduct electricity has to have free electrons to carry this current. Some substances such as the metals cannot be used as solids for electrolysis. Although they are good conductors, when they are solid they do not have the free electrons that are needed for electrolysis because they are solid but they can be used in electrical circuits even though they are solid. Whereas, when they are molten, the electrons are free to move and carry current.
The atoms are free and even if electrons have to pass through, they can do so easily. This is true for the ionic compounds. These compounds act like this because their atoms are all combined by transfer of electrons and when they are molten, these atoms are free to carry current because there is no longer a bond between the substances. The electrons that are arranged on the outer shell of the atoms are usually found to be the free electrons. This is because they are far away from the nucleus and thus can be used to carry charges more easily and so they are used.
Covalent substances do not usually conduct electricity because the electrons are all shared between the substances and there are no extra or free electrons that can be used to carry charges. Plastic is an example of a covalent substance. In circuits an ammeter is used to measure the current, which is measured in amps, and it is connected in series always. Amps is a measure of the amount of current flowing through the circuit. If the current given is low, then a milliammeter is used. However, for voltage, the voltmeter is used and is connected in parallel.
It measures the voltage or potential difference in volts. Voltage is the ‘push’ that is applied onto the electrons so that they move through the circuit. The battery or cell provides an electromotive force. This force pushes the electrons into the circuit. From this perhaps we can understand that when the voltage increases, the amps also might increase. From the readings of these two components, graphs are drawn. When we have to check if the certain substance conducts we can place it in a circuit. When a metal is placed in the circuit, an electric field is created.
This electric field has charges and these charges have forces on them. So the electrons are accelerated and gain velocity and energy. They will collide with atoms that are vibrating in their lattice site and give some of their energy to it. When they slow or stop the energy is again provided to them by the electric field and they accelerate. The charges thus move to one side and this called a current. The circuit that can be used should consist of a power (d. c. supply), connecting wires, a bulb and the object to be tested. The bulb is used to show whether the substance conducts or not.
If correct accurate reading regarding the current and the voltage has to be taken, then the ammeter is connected in series and the voltmeter in parallel. This way we will know how much current is flowing through the circuit if the object is a conductor. If the object is an insulator then the bulb will not light up and the ammeter will not show any reading. This is a conductor when no potential difference is applied. When a potential difference is applied between the ends of the conductor, as shown in the previous circuit, they all line up to move to one side.
This is the structure after the potential difference is applied. The resistance in metallic conductors increases as temperature increases. The resistance increases because the atoms of the metal start to vibrate and so making it difficult for electrons to pass through. This increases resistance. So whatever the amount of electrons provided, the current will decrease because the resistance has increased. In semiconductors the conductivity varies from the types of semiconductors. There are two types intrinsic and extrinsic semiconductors. This way there is no definite rule for these materials.
So this would have to be seen only when I deal with the semiconductors separately. Silicon and germanium are semiconductors. Semiconductors are materials in which the amount of current increases with temperature. So this means that they are better to use if the temperature is high. Since we have now discussed the conductivity of certain substances and the free electron theory, I would now like to introduce the ohmic and non ohmic conductors. Ohm’s Law states that the current flowing through a certain conductor is proportional to the voltage given that physical factors such as temperature are kept under control and constant.
Some other factors also affect the ohmic conductors. There are normally two types of conductors. The two types of conductors are ohmic and non ohmic. Ohmic Conductors such as a pure metal such as copper or tungsten obey Ohm’s Law given that the temperature and pressure at kept low and constant. The others that do not obey Ohm’s Law are called Non Ohmic Conductors. Conductors such as pure metals are ohmic conductors. In this case the ohmic conductors have to be kept under constant pressure and constant temperature for them to behave as ohmic conductors.
The resistance does not vary according to the current, it remains constant. The current flowing through it also has to be kept less because then it will lose its property of being an ohmic conductor. The temperature at which the metal is used will change as the current flowing through it. To prevent this we have to keep the current value low otherwise it will lose its property of being an ohmic conductor. This is called the heating effect. The current that is carried through the metal is due to the free electrons so when the amount of current passing through the wire.
When the current is passed through the atoms vibrate more and collide with some of the other atoms and then give out this kinetic energy. Thus as the current flows the kinetic energy of these atoms is increased. Thus this energy is lost as heat and so makes it difficult for the electrons to pass through. The amplitude of the vibrations of the atoms increases and more ‘collisions’ with atoms are caused by the electrons. Therefore the resistance increases with temperature. This means that it is no longer an Ohmic conductor.