The Resistivity Of Materials

We know that materials are classified into three types: conductors, semiconductors, and insulators. Conductors allow electricity to flow through them. Before we go into electrical resistivity in this article, let’s define electrical conductivity and its terms.

Electrical conductivity is a material quality defined as the quantity of electrical current that a material can convey. Specific conductance is another name for electrical conductivity, and the SI unit is Siemens per metre (S/m). It is also characterised as the current density to electric field strength ratio. The Greek letter σ is used to signify it.

What is Resistance?

We know that the flow of electric current in a circuit is analogous to water flow in a river. Boulders, branches, and other particles act as barriers to the water’s movement in a river. Similarly, resistivity of a wire depends on elements in a circuit that may block the flow of electrons. Resistance is the attribute of resisting the flow of electrons or electricity. The Ohm is the unit of resistance. Resistance of one Ohm equals one volt per ampere. We know from Ohm’s law that R = V/I, where V denotes voltage and I denotes current.

The main functions of Resistors are used to resist or regulate the flow of electrons via a conductor. They supply no current to the circuit. They can lower the voltage and current that flow through the course. As a result, resistors are considered passive devices. The majority of resistors are composed of a carbon, metal, or metal oxide sheet.

Resistivity of Materials

When determining a material’s resistivity, we look at how much resistance it has per unit length and area. It is the material property that acts as an impediment to the flow of charge or electric current. The ohmmeter is the unit of resistivity. We already know that R = ρL/A. Thus, we may deduce the resistivity expression from this formula. ρ = RA/L, where R denotes resistance in ohms, A represents the cross-sectional area in square metres, and L indicates length in metres. When the length L and the site A are equal, we can say that the resistivity equals the resistance. 

Thus, resistivity can be defined as a material’s particular resistance. When a thick  wire is used, the resistance decreases. The resistance increases when the wire is thin due to the smaller cross-sectional area. The greater the length of the wire, the more is the resistance. When the wire’s size is reduced, the resistance reduces proportionately.

A material with high resistivity has a high resistance to electron flow. A material with a low resistivity has a low resistance, allowing electrons to flow freely through it. Copper and aluminium are both low-resistance metals. Conductors with low resistivity are considered to be good conductors. Insulators have high resistance. Semiconductors have a resistivity that is between that of conductors and that of insulators. Because gold is an excellent conductor of electricity, it has a low resistivity. 

Glass is an excellent insulator, preventing the flow of electrons. As a result, it has a high resistance. Because silicon is a semiconductor, it allows for the partial mobility of electrons. Silicon’s resistivity is somewhere between Glass and gold. Perfect conductors have zero resistivity, while perfect insulators have infinite resistivity.

Electrical Resistivity: What Is It?

Electrical conductivity is inversely proportional to electrical resistance. The capacity of a material to resist the passage of current is assessed using this metric.

• Electricity travels easily through metals. As a result, their resistance is low.
• Rubber, glass, graphite, plastic, and other insulators have a far higher resistance than metallic conductors.
• A semiconductor is a material that sits in the middle of the two other categories. In addition to temperature, contaminants in the material reduce the resistivity of the material.

Resistivity Variation with Temperature: Resistivity Of Materials

Their atomic structure determines the resistivity of materials. Thus, by varying the temperature, we may alter the resistivity of materials. The valence electrons are known to be weakly linked to the nucleus. Although electrons collide with metal atoms at room temperature, free electrons flow freely. Thus, as long as there is any resistance in the metal, the current continues to flow.

As the temperature increases, the metal atoms begin to vibrate, causing a random motion. Thus, the unbound electrons could move much more slowly than they would at room temperature. When the temperature rises, the obstruction increases, increasing resistance. When atoms begin to vibrate with increased amplitude, collisions become more frequent. Thus, the drift velocity drops, and the current begins to diminish.

Electrons in nonmetals are strongly linked to the nucleus. When the applied temperature is too high, the electrons separate from the atoms and exit the fraction for conduction. As a result, the conductivity rises. When conductivity increases, resistance reduces, and hence current flow increases.

A material heats up when a current flows through it. When the temperature fluctuates, so does its resistance. The effect will be too tiny for the majority of resistors. However, for some other resistors, the product is relatively high. Therefore, temperature sensors can be made using resistors with a substantial effect. We can determine the resistance of a material by applying a known voltage across a resistor and measuring the current. As a result, we can determine the substance’s temperature to which the resistor is attached. As a result, it can be used as a temperature sensor.

Unit of Resistivity

Factor affecting the resistivity of materials

The following are the elements that influence material resistivity:

• Materials nature
• Temperature

Conclusion

Water flows through a river in the same way as electricity travels through a circuit. Branches and other debris in a river rock impede water movement. Similarly, the passage of electrons is blocked by various components of a circuit. Also, The electric shocks must be terrifying! So that is why wires are covered with plastic. Plastic cables do not conduct electricity. Nevertheless, what exactly is the reason behind this? This is due to plastic being an insulator.