Ultimate Guide on Resistivity and Electrical Conductivity We know what the electric wires are made of; they are either made of copper or aluminum. We also know that Gold and Silver would have been a better choice, had they been cheaper. However, the question is what makes them suitable for the same? Why don’t we see lead wires? The answer lies in the very basic property of these materials, namely their resistivity and electrical conductivity. This article explains the essential concepts of resistivity and electrical conductivity. Resistivity and conductivity are actually two sides of the same coin, if you understand one, you will get the other as well. What is Resistivity? The resistivity of a material is the measure of its property due to which it opposes the flow of electrons through it. As we know, the flow of electrons leads to current flow, therefore if a material opposes the flow of electrons, the current that can pass through it is limited. Some materials oppose the flow more than others. This is due to the varied atomic structure of different materials. In order to understand resistivity better, let us first revise the concept of ohm’s law. OHMS LAW: The ohm’s law states that when a voltage (a potential difference) is applied across a conductor, current starts to flow through it. This current is directly proportional to the voltage. Numerically, Ohms law can be written as: V α I; where V = voltage, I= Current through the conductor Or V= RI ……. equation (1) Here, R = Constant, known as Resistance. This resistance restricts the amount of current or we can say that it restricts the amount of electron flow. This means that the conductor resists the current flow to some extent. SI UNIT OF RESISTANCE R = ohm denoted by Ω. = Volt/Amp. In order to change the amount of current, that is the amount of electrons flowing, we can just vary the resistance value. You may assume, from equation 1, that to increase the resistance, we just have to increase the voltage applied. Well, you are wrong!, as according to the ohms law, an increase in voltage applied will only result in an increase in current( voltage and current are proportional to each other, remember! And ‘resistance’ R is a constant for any given conductor of fixed length and area) and would give us no change in resistance. Just look at the figure below that shows voltage versus current graph. It is a straight line with a slope R. Since now we know changing the applied voltage won’t help changing the resistance, then what can be done to change it? For that, let us look into the factors that affect the resistance of the conductor. Factors affecting Resistivity: The resistance of a material is its ability to oppose the flow of electrons through it. It depends on the physical dimensions; that is its Length and Area of the cross section. Other factors include temperature and type of material used to make the conductor. First, let us analyse the effect of the length and area of cross-section on the resistance of a conductor. For that, we can take example – a conductor of length L and area of cross-section A having a resistance R. Case 1: Changing Length of Conductor (and Area of cross section kept constant). From the electromagnetic theory, whenever a voltage, V is applied across a conductor, an electric field, E is formed. The two are related by the following equation: V=E.L ….. equation (2) L is the length of...
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