Resistance - juxtapix/IMA_E4I GitHub Wiki
Reading: 2.5 Resistance, Resistivity, Conductivity pg.23
Resistance, Resistivity, Conductivity
Resistance is the ability of any component to restrict the flow of electricity. In the plumbing analogy, resistance is like the diameter of the pipe that the water flows through. The smaller the diameter, the higher the resistance, limiting the amount of water that is able to flow.
- Most components has a measured resistance, even wires.
- Resistance is measured in ohms, or the symbol omega Ω.
- Resistance is added to a circuit by the use of resistors.
Resistance was defined in 1826 by Georg Simon Ohm when he published his study on the resistance of different materials. He found a linear correlation between the voltage applied and the amount of current that flowed through the materials. He found that resistance is the ratios of voltage and current.
His observations lead to the creation of the fundamental Ohms law: R = V/I
How the Shape of a Conductor Affects Resistance
A couple factors determine the resistance of a component: its shape and its material. For any given material with similar applied voltage, the length and cross section area will either increase or decrease the resistance. Doubling the length of a material will double its resistance, while doubling the cross section has the opposite effect and will decrease the resistance.
Conductors, Semiconductors and Insulators
Every material used in a circuit has different resistance and can be categorized in 3 major groups: Conductors, Insulators, and Semiconductors.
Conductors
Conductors have very low resistance. These include carbon and metals like aluminum, silver and copper. Wires, electrical contacts, and lamp filaments are made from metals to take advantage of their excellent conductive properties. Resistors are made from carbon or long coils of thin wire to increase the resistance.
Insulators
Insulators have very high resistance as they insulate against the flow of electricity. They are usually made of plastics, rubber, glass, etc. Wires are usually covered with a layer of insulator material like PVC to isolate them from making contact with other wires and components.
Semiconductors
Semiconductors have on average moderate resistance. They are most commonly made of silicon and sometimes germanium. Semiconductors are essential components used in most electronic circuits because based on certain conditions, they can act as a conductor or an insulator. Semiconductor materials are the building blocks of components like diodes, transistors, thermistors, phototransistors, photoresistors, and integrated circuits.
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