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Ohm’s law is key to understanding how resistance works. The relationship between the current flowing in a circuit and the potential difference across its terminals was found by Georg Simon Ohm In 1827. He stated that when the temperature remains constant, the current in a circuit is directly proportional to the potential difference across the ends of the metallic wire in a circuit. This is known as Ohm’s law.
In mathematical terms, V ∝ I
or, V = IR
R is called resistance. It is constant at a certain temperature for a certain metallic wire.
What is resistance?
Resistance is the property of a conductor which counteracts the flow of charges across it. Ohms (Ω) is used to measure resistance.
If Ohm’s law is considered, V = IR
For a potential difference of 1V across the ends of a conductor and a current of 1A flowing through it, the resistance of the conductor is 1 Ω.
From Ohm’s law, it can be seen that the current in a resistive circuit is inversely proportional to the resistance. The resistance works in such a way that the opposition against the flow of current is larger when the resistance is greater. The magnitude of electrical energy transferred through the conductor is reduced depending on how resistance works. The atoms, electrons, and impurities in the metal absorb the energy when there is a collision and turn it into heat.
What causes resistance?
Resistance works at the molecular level, opposing the flow of current. Consider a metal conductor like aluminium. The outermost shells of the aluminium atom contain free electrons. There is the random
movement of the free electrons from atom to atom regularly.
However, when a device such as a battery is used to apply a voltage across the conductor. The free electrons start moving from the negative terminal to the positive terminal of the battery. The free electrons start flowing due to the electric current, which is nothing but the rate of flow of electric charge.
The electrons moving in the direction of the positive terminal clash with other electrons, atoms, and impurities in the metal. This is because the imperfections in the atomic lattice of metals cause the scattering of electrons. The resistance in the conductor works due to these collisions. Heat is generated from the voltage supplied as the electrons clash with atoms and other particles.
What are the factors affecting resistance?
Length of the conductor
The resistance varies directly proportional to the length of the conductor. If the conductor is longer, there will be more resistance. This is because resistance is caused by the collision between electrons and atoms present in the conductor. In this case, if the conductor is longer, there will be more collisions leading to higher resistance.
The cross-sectional area of the conductor
The resistance of a conductor is inversely proportional to the area of the cross-section of the conductor. In this case, the resistance decreases when the area of the conductor increases when the area of the conductor decreases. This is because a larger area allows more current to flow through the conductor, decreasing the resistance.
Nature of material
Low resistances are seen in electrical conductors, such as metals. These allow the electric charge to flow freely through the material without immense opposition. A conductor is said to be ideal if it has zero resistance. High resistances are seen in electrical insulators. An insulator is said to be ideal if it has limitless resistance. There would be no current flowing through, and it would not dissipate any energy as heat.
Resistivity
Every material has a property called resistivity. All materials have electrons that move freely between atoms and electrons that cannot move freely and are tightly linked to the atom. Free electrons are required to move through the conductor to facilitate the flow of charge. When a material has lower free electrons and more linked electrons, it is a poor conductor and will have a higher resistivity. The converse is also true; a material with more free electrons in its atoms will be a good conductor with low resistivity.
Temperature
A cooler conductor provides less resistance to the flow of current through it than a warmer conductor does. This is because the atoms in the metal lattice start vibrating harder as the temperature increases. This leads to more collision between the electrons and atoms, which leads to higher resistance. Cool conductors do not vibrate as much and have lesser resistance. Superconductors that are cooled to very low temperatures have almost no resistance.
How is resistance used?
When a material has high resistance, it is hard for electricity to pass through it. The harder it is for electricity to pass, the more energy that is wasted.
Even though it leads to loss of energy, uses of resistance. Resistance is used to heat things through the use of heating elements. The temperature of heating elements increases to a great extent when an electric current flows through them. These hot elements are then used to boil water or toast bread. These heating elements are used in appliances like electric kettles, electric radiators, electric showers, coffee makers, and toasters.
Another use of resistance is in specialised elements called resistors. They are placed into a circuit for the explicit role of generating an accurate amount of resistance. Resistors are used to limit and regulate current flow, divide voltages, adjust signal levels, and bias active elements in circuits.
Conclusion
Resistance is the property of a conductor which counteracts the flow of charges across it. When a battery applies a voltage across a conductor, the free electrons start moving towards the positive terminal and clash with other electrons, atoms, and impurities in the metal. This is due to the imperfections in the atomic lattice of metals, which cause the scattering of electrons. The resistance in the conductor works due to these collisions. The resistance depends on the length, cross-sectional area, material, and temperature of the conductor. Resistance can be used to heat things or to restrict the flow of current in a circuit.
