Ohmic resistance is a measure of an electrical circuit's resistance to current flow. It can also be referred to as ohmic resistance or electrical resistance. Resistance is measured in ohms, which is represented by the Greek letter omega (O). There are two types of resistors in general. Set Resistors and Variable Resistors.
Set resistors are determined before they are sold, so their values are known ahead of time. They can only be changed by replacing the whole unit. Variable resistors can be adjusted after they are installed in a project; thus their values can be fine-tuned as needed. The two main types of variable resistors are mechanical and electronic. Electronic variable resistors use a voltage divider network to divide a fixed reference voltage from a battery or power source into smaller voltages that vary depending on the position of a wiper contact or other type of switching device such as a triode for alternating current (triac). This division produces a higher voltage when the wiper contact is away from either end of the resistor and lower voltages when it is near one end or the other. Mechanical variable resistors use a spinning disk with notches or holes that interrupt light beams coming from opposite sides of the disk. The light beam that reaches the center hole determines the output value of the resistor.
Resistance can be used within circuits to control how much current flows through them.
The property of a substance that impedes the flow of electric current is referred to as resistance. Some compounds are more resistant to current flow than others. A conductor is a device that has an extremely low resistance to current flow. The property of substances to resist current flow is referred to as resistivity. There are two types of resistivity: conductive and nonconductive.
Conductors such as copper have the ability to transmit electricity without any loss. In contrast, nonconductors such as glass have very high resistance to the flow of electricity. One important application for resistance is in measuring instruments called ohm's meters. These are used by electrical technicians to measure voltage and current values in circuits.
Resistance can also be defined as the opposition that exists between two different sets of electrons moving through a conductor toward opposite ends of this conductor. The more effort it takes to move these electrons through the conductor, the higher its resistance will be. Conductors are materials that allow electrons to pass easily from one end to the other; otherwise they would be unable to carry electric current. The term "conductor" may imply a path only for electrons but not for photons (light particles), so some scientists include molecules as conductors. For example, carbon atoms in polyacetylene form a chain that allows electrons to pass easily along it, so it becomes a conductor when exposed to radiation.
In electronics and electromagnetism, an object's electrical resistance is a measure of its resistance to the flow of electric current. The ohm (O) is the SI unit of electrical resistance, whereas siemens (S) is the SI unit of electrical conductance (formerly called "mho"s and then represented by).
Electrical resistance arises from the tendency of electrons to move away from any location where there is a high concentration of electrons (such as near the positive terminal of a battery), and this movement requires energy. The more electrons that are moved, the higher the resistance becomes. At very low currents, all materials exhibit some degree of resistance. But at high currents, metal wires become so hot that they begin to emit radiation, which can damage other devices or cause burns to touch them. In fact, electricity flows more freely through a metal wire when it is warm than when it is cold because the resistance increases with temperature. This is why heaters use metal wires as their primary source of power - the wires get hot because they resist the flow of current.
Resistance can be defined as the proportional reduction in potential difference that results from a given change in current. For example, if the current through a resistor increases by 100%, then the voltage across it increases by 10%. Resistance therefore has the same units as voltage: Ohms (Ω). It is a property of all electrical components that impede the flow of current, such as wires, cables, circuit boards, and batteries.
Electrical resistance: The resistance provided by an electrical conductor to the flow of a current through itself, resulting in the conversion of electrical energy into heat and radiation. The ohm is the SI-derived unit of resistance. The higher the resistance, the more energy it will take to drive a current through it.
Examples: Your house wiring has a high resistance because many wires are insulated with only thin layers of insulation between them. This means that a lot of energy is required to drive a current through the wire. The power line coming into your house is also very resistive because it passes over a wide area of land before it gets to you. Telephone lines are also quite resistant because there are many circuits within them that contain multiple strands of wire wrapped around each other (which increases resistance).
Resistance can also be caused by friction between two surfaces moving relative to one another. For example, if two metals with different coefficients of thermal expansion were pressed together, then they would create heat when powered by an electric current and eventually they would need to be replaced due to wear and tear. This form of resistance is called "thermal resistance" and its value is usually expressed in kelvins or °C. /W.
Finally, resistance can be caused by the presence of impurities in a material.
Electrical resistance is a number that quantifies the resistance a device or substance provides to the flow of electric current. A resistor is a type of electric component that provides the necessary resistance in a circuit. The resistance of a material depends on its composition and structure. Resistor values from 1 megohm (MΩ) up to many tens of gigaohms are available today, with more coming out every year.
Resistance is used to control current flow through a circuit. The greater the resistance, the less current will flow. The least resistant circuit path will be used for current flow unless another path is provided by a switch, transformer, or other component. The term "resistance class" refers to the relative resistance of two circuits that use different materials but which perform the same function. For example, a resistive heater needs current to pass through it to keep it warm; if the current is too low, it won't get hot enough. A thermometer needs very little current to measure temperature, so it has a low resistance compared to a heater, and would be classified as "class 10" if measured with standard testing methods.
The resistance of electronic components varies depending on their make and model. It can also vary depending on how they are mounted or connected together. A general rule is that the higher the resistance value, the better for heat dissipation.