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Introduction
Electrical resistivity and conductivity are two sides of the same coin, but they’re essential concepts to understand when studying electronics. They’re two different ways of expressing the same fundamental physical property: how easily electric current flows through a substance.
Electrical resistivity is a material attribute that indicates how much it resists the flow of electric current, whereas conductivity measures how easily current flows. With electrical conductivity being the inverse of resistivity, a thorough understanding of both is essential for solving difficulties in electronics physics. Let us dive into more details to understand the concept of electrical resistivity and conductivity closely.
Ohm’s Law
When a voltage (V) source is supplied between two locations in a circuit, the presence of a potential difference between these two places encourages an electrical current (I) to flow between them. The quantity of current that can flow is limited by the resistance (R) present. To put it another way, voltage facilitates current flow (charge movement), whereas resistance inhibits it.
Ohms always measures electrical resistance, which is represented by the Greek letter Omega. When a voltage (V) source is supplied between two locations in a circuit, the presence of a potential difference between these two places encourages an electrical current (I) to flow between them. The quantity of current that can flow is limited by the resistance (R) present. To put it another way, the voltage encourages. Voltage facilitates current flow (charge movement), whereas resistance inhibits it.
Ohms always measures electrical resistance, which is represented by the Greek letter Omega.
Electrical Resistivity
The resistivity of a material is a fundamental element in determining the electrical resistance of a conductor, and it is the part of the resistance equation that accounts for different materials’ characteristics.
In order to explain electrical resistance we can use a simple example. Assume the flow of electrons (current electric carriers) across a wire is represented by marbles flowing down a ramp: If you put obstacles in the way of the ramp, you’ll encounter resistance. As marbles collided with the barriers, they lost some of their energy, causing the total flow of marbles down the ramp to slow down.
The effect of going through a paddle wheel on the speed of a current of water is another comparison that might help you grasp how resistance affects current flow. Again, energy is transferred to the paddle wheel, causing the water to move more slowly.
The reality of current flow through a conductor is closer to the marble example because electrons travel through the material but are slowed by the lattice-like structure of the nucleus of the atoms.
A conductor’s electrical resistance is defined as:
R = LA
Where is the material’s resistivity (which varies depending on its composition), L is the conductor’s length, and A is the material’s cross-sectional area (in square meters). According to the equation, a longer conductor has a higher electrical resistance, while one with a larger cross-sectional area has lower resistance.
Factors Determining Resistivity
- Nature of the substance:
According to their resistivity, materials are classified as insulators, conductors, and semiconductors, among others.
Insulators have high resistivity, whereas conductors have very low resistivity.
- Temperature:
As the temperature of the material rises, the resistivity increases as well.
- Cross-sectional area:
A wire’s resistance R is inversely related to its cross-sectional area A, as follows:
R α 1/A…. (1)
It signifies that a thicker wire has less resistance than a thinner wire. We get the following when we combine equations R α L….. and (1)
R α L/A
R=ρL/A….(2)
Where is the proportionality constant, also known as particular resistivity. The conductor’s nature determines its value; for example, copper, iron, tin, and silver have distinct values. We can deduce the following from equation (3):
ρ= R A /L… (3)
Electrical Conductivity
While both electrical resistance (R) and resistivity (or particular resistance) are a function of the material’s physical constitution, as well as its physical shape and size as expressed by its length (L) and sectional area (A), The ease with which electric current can pass through a material is referred to as conductivity or specific conductance.
Conductance (G) is the reciprocal of resistance (1/R), with the siemens (S) as the unit of conductance, and is denoted by the upside-down ohms sign mho. The resistance of a conductor with a conductivity of 1 siemens (1S) equals 1 ohm (1). As a result, doubling the resistance reduces the conductance, and vice versa: siemens = 1/ohms, or ohms = 1/siemens.
While the resistance of a conductor reveals how much resistance it provides to the flow of electric current, the conductance of a conductor indicates how easily it allows electric current to flow. As a result, metals like copper, aluminium, and silver have very high conductance ratings, suggesting good conductors.
The reciprocal of resistivity is conductivity (Greek letter sigma). The unit of measurement is siemens per metre (S/m). R can be expressed as: since electrical conductivity = 1/ , the preceding formula for electrical resistance.
Electrical Conductivity Affecting Factors
Three primary factors influence the electrical resistivity and conductivity of a substance:
- Cross-Sectional Area: A large cross-sectional area allows more current to travel through a material. A narrow cross-section, likewise, hinders current flow.
- The Conductor’s Length: A short conductor allows for faster current flow than a long conductor. It’s similar to getting a large group of people through a hallway.
- Temperature: causes particles to vibrate or move more as the temperature rises. Because the molecules are more prone to come in the way of current flow, as this mobility (temperature) increases, conductivity diminishes. Some materials are superconductors at extremely low temperatures.
Resistor
A resistor is an electrical component that causes resistance in current flow. They can be found in practically all electrical networks and electronic circuits. Resistance is expressed in ohms. When one ampere (A) current passes through a resistor with one volt (V) drop across its terminals, the resistance is measured in ohms. The voltage across the terminal ends determines the current. Ohm’s law can be used to express this ratio:
R=VI
Resistors are used in a variety of applications. Examples include limiting electric current, voltage division, heat generation, matching and loading circuits, gain control, and constant time setting. They have resistance levels spanning more than nine orders of magnitude and are commercially available. They can be smaller than a square millimetre for electronics or used as electric brakes to dissipate kinetic energy from trains.
Discuss Resistor Colour Coding
Several coloured bands around the component body represent the resistance value and tolerance. This electronic component labelling approach was first developed in the 1920s. Because printing technology was still in its infancy, printing number codes on small components was impossible. The colour scheme is still used today for most axial resistors up to one watt. A four-colour band example is illustrated in the diagram above. The two first bands in this example determine the resistance value’s significant digits, the third band is the multiplying factor, and the fourth band is the tolerance. A resistor colour coding chart or a resistor colour code calculator can be used to look up which colour symbolises which number.
Conclusion
From this information, we have learnt the concept of Electrical resistivity and conductivity. Resistivity is a property of a substance or conductor that determines how well it carries electrical current, as we learned in this resistivity tutorial. We’ve also seen that a conductor’s electrical resistance (R) is affected not only by the substance it’s constructed of, such as copper, silver, or aluminium, but also by its physical dimensions.
The effectiveness of the earth grounding system for an electrical power and distribution system is strongly dependent on the resistivity of the earth and soil material at the position of the system ground; hence resistivity is also significant in power distribution systems.
