Current is equal to voltage divided by resistance. commonly written as I = v / r. AnswerParty
Analogue electronics (or analog in American English) are electronic systems with a continuously variable signal, in contrast to digital electronics where signals usually take only two different levels. The term "analogue" describes the proportional relationship between a signal and a voltage or current that represents the signal. The word analogue is derived from the Greek word ανάλογος (analogos) meaning "proportional".
Electrical resistance and conductance
A physical quantity (or "physical magnitude") is a physical property of a phenomenon, body, or substance, that can be quantified by measurement.
The electrical resistance of an electrical conductor is the opposition to the passage of an electric current through that conductor; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical notion of friction. The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in siemens (S).
An object of uniform cross section has a resistance proportional to its resistivity and length and inversely proportional to its cross-sectional area. All materials show some resistance, except for superconductors, which have a resistance of zero.
Voltage drop describes how the supplied energy of a voltage source is reduced as electric current moves through the passive elements (elements that do not supply voltage) of an electrical circuit. Voltage drops across internal resistances of the source, across conductors, across contacts, and across connectors are undesired; supplied energy is lost (dissipated). Voltage drops across loads and across other active circuit elements are desired; supplied energy performs useful work. Recall that voltage represents energy per unit charge. For example, an electric space heater may have a resistance of ten ohms, and the wires which supply it may have a resistance of 0.2 ohms, about 2% of the total circuit resistance. This means that approximately 2% of the supplied voltage is lost in the wire itself. Excessive voltage drop may result in unsatisfactory operation of, and damage to, electrical and electronic equipments.
National and local electrical codes may set guidelines for the maximum voltage drop allowed in electrical wiring, to ensure efficiency of distribution and proper operation of electrical equipment. The maximum permitted voltage drop varies from one country to another. . In electronic design and power transmission, various techniques are employed to compensate for the effect of voltage drop on long circuits or where voltage levels must be accurately maintained. The simplest way to reduce voltage drop is to increase the diameter of the conductor between the source and the load, which lowers the overall resistance. More sophisticated techniques use active elements to compensate for the undesired voltage drop.
A voltage ladder is a simple electronic circuit consisting of several resistors connected in series with a voltage placed across the entire resistor network. Voltage ladders are useful for providing a set of successive voltage references, for instance for a Flash analog-to-digital converter.
A voltage drop occurs across each resistor in the network causing each successive "rung" of the ladder (each node of the circuit) to have a higher voltage then the one before it. Ohm's law can be used to easily calculate the voltage at each node. Since the ladder is a series circuit, the current is the same throughout, and is given by the total voltage divided by the total resistance (V/Req), which is just the sum of each series resistor in the ladder. The voltage drop across any one resistor is now given simply by I*Rn, where I is the current calculated above, and Rn is the resistance of the resistor in question. The voltage referenced to ground at any node is simply the sum of the voltages dropped by each resistor between that node and ground. Alternatively, you can use voltage division to determine node voltages without having to calculate the current directly. By this method, the voltage drop across any resistor is V*Rn/Req where V is the total voltage, Req is the total (equivalent) resistance, and Rn is the resistance of the resistor in question. The voltage of a node referenced to ground is still the sum of the drops across all the resistors, but it's now easier to consider all these resistors as a single equivalent resistance RT, which is simply the sum of all the resistances between the node and ground, so the node voltage is given by V*RT/Req.
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