External Resistor
External Resistor - Related Videos
11:34
Series and Parallel Resistors
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2023
Source: Yong P. Chen, PhD, Department of Physics & Astronomy, College of Science, Purdue University, West Lafayette, IN This experiment demonstrates how current is distributed in resistors connected in series or parallel, and thus describes how to calculate the total "effective" resistance. Using Ohm's law, it possible to convert between the voltage and current through a resistance, if the resistance is known. For two resistors connected in series, (meaning that they are wired one after the...
01:10
Resistors In Series
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2023
A resistor is an ohmic device that limits the flow of charge in a circuit. Most circuits have more than one resistor. If several resistors are connected together and connected to a battery, the current supplied by the battery depends on the equivalent resistance of the circuit. The equivalent resistance of a combination of resistors depends on both their individual values and how they are connected. The simplest combination of resistors is the series combination. In a series circuit, the...
01:18
Combination Of Resistors
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2023
Electrical devices in any circuit can be connected either by series or parallel connections. Additionally, circuits can be connected involving both of these connections, known as combination or complex circuits. As these circuits have complex resistor connections, it is necessary to identify different parts as either series or parallel connections, then the whole combination of series and parallel resistors can be reduced to a single equivalent resistance. With the known equivalent resistance...
01:23
Resistors In Parallel
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2023
Resistors are in parallel when one end of all the resistors are connected to a continuous wire of negligible resistance and the other end of all the resistors are also connected to one another through a continuous wire of negligible resistance. In the case of a parallel configuration, the potential drop across each resistor is the same. Current through each resistor can be found using Ohm’s law, I = V/R, where the voltage is constant across each resistor. The sum of the individual currents...
01:31
Resistor in an AC Circuit
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2023
An alternating emf or voltage source is needed to supply an alternating current (AC) to a circuit. A coil of wire rotating in a magnetic field at a constant angular speed represents such a source. It also generates a sinusoidal alternating emf and serves as an industrial alternator. One-way current through the meter is measured using diodes. A diode is a device with better conductivity in one direction compared to the other; in its ideal state, it has zero resistance in one direction and allows...
FAQs
The key operating relationship is the voltage-current proportionality described by Ohm’s law. For a chosen resistance, increasing current produces a corresponding increase in voltage across the component, while changing the resistance changes that relationship. This predictable behavior lets engineers set circuit conditions rather than allowing current and voltage to vary without control, supporting stable operation and accurate measurements.
The power rating indicates how much electrical energy the resistor can convert into heat under operating conditions. A resistance value may produce the desired voltage or current relationship, but the component must also tolerate the resulting power. Choosing an appropriate rating helps prevent unsafe operation, supports circuit stability, and improves the reliability of the engineering design.
Pull-up and pull-down configurations help establish defined voltage relationships in a circuit. Their function complements biasing, because the resistor provides a controlled electrical influence rather than leaving the desired condition unspecified. Engineers select these arrangements when a circuit needs a predictable signal or operating state, making them useful in designs involving integrated circuits and signal conditioning.
An external resistor can limit current before it reaches a light-emitting diode or an integrated circuit. This reduces the chance that the connected component experiences an excessive current condition and also helps establish the intended electrical relationship in the circuit. The resistance and power rating must both suit the operating conditions to support protection and reliable function.
Selection starts by identifying the voltage and current relationship the circuit requires, then using Ohm’s law to choose a suitable resistance. Engineers also evaluate the electrical energy converted into heat and select a power rating that accommodates the operating condition. This combined check avoids choosing a value that meets current-control needs but cannot safely handle the associated power.
External resistors serve several engineering purposes beyond simple current control. They support signal conditioning, biasing, pull-up and pull-down arrangements, defined loading, and protection for components. They can also improve measurement accuracy by creating predictable voltage and current relationships. These applications make resistor selection relevant to circuit stability, safety, and the controlled operation of connected devices.