Electrical Resistance

Introduction

Electrical resistance is a measure of the degree to which an object opposes the passage of an electric current. The SI unit of electrical resistance is the ohm (Ω). It is named after Georg Ohm, a German physicist who formulated Ohm's Law, which states that the current passing through a conductor between two points is directly proportional to the voltage across the two points.

Fundamental Concepts

Ohm's Law

Ohm's Law is a fundamental concept in the study of electrical resistance. It states that the current passing through a conductor between two points is directly proportional to the voltage across the two points. This relationship is often expressed in the formula I = V/R, where I is the current, V is the voltage, and R is the resistance.

Resistivity

Resistivity is a property of a material that quantifies how strongly it resists the flow of electric current. It is denoted by the Greek letter rho (ρ), and its SI unit is the ohm-meter (Ω.m). Resistivity is a fundamental property of materials, and it is temperature dependent.

Conductivity

The reciprocal of resistivity is electrical conductivity. It is a measure of a material's ability to conduct an electric current. The SI unit of electrical conductivity is the siemens per meter (S/m).

Factors Affecting Resistance

Several factors can affect the resistance of a conductor. These include the material the conductor is made of, its length, its cross-sectional area, and its temperature.

Material

The type of material a conductor is made of significantly affects its resistance. Some materials, such as copper and silver, have low resistivity and therefore low resistance. These materials are good conductors of electricity. Other materials, such as rubber and glass, have high resistivity and therefore high resistance. These materials are good insulators.

Length

The length of a conductor also affects its resistance. The longer the conductor, the higher its resistance. This is because the electrons moving through the conductor encounter more atoms and thus more resistance.

Cross-Sectional Area

The cross-sectional area of a conductor affects its resistance as well. The larger the cross-sectional area, the lower the resistance. This is because a larger cross-sectional area allows more paths for the electrons to take, reducing the overall resistance.

Temperature

Temperature can also affect the resistance of a conductor. As temperature increases, so does resistance. This is because the atoms in the conductor vibrate more at higher temperatures, which increases the likelihood of collision with the electrons and thus increases resistance.

Applications of Resistance

Electrical resistance has many practical applications. It is used in a variety of electrical and electronic devices, including resistors, thermistors, and LEDs.

Resistors

Resistors are devices that are used to control the flow of electric current in an electronic circuit. They are designed to have a specific resistance, which can be used to limit the current, divide voltage, or create a voltage drop in a circuit.

Thermistors

Thermistors are a type of resistor whose resistance varies with temperature. They are often used in temperature sensing devices.

LEDs

LEDs, or light-emitting diodes, are semiconductor devices that emit light when an electric current passes through them. The resistance of the semiconductor material controls the amount of current that can pass through the LED, which in turn controls the brightness of the light.