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Types of Resistor Carbon Composition and Wire Wound Resistor
- Sep 21, 2017 -

Definition of Resistor

resistor offers resistance to the flow of current. The resistance is the measure of opposition to the flow of current in a resistor. More resistance means more opposition to current. The unit of resistance is ohm and it is represented as Ω. When one volt potential difference is applied across a resistor and for that one ampere of current flows through it, the resistance of the resistor is said to be one Ω. Resistor is one of the most essential passive elements in electrical and electronics engineering.

Resistor

It is some time required to introduce electrical resistance in different circuit to limit the current through it. Resistor is an element of circuit which does the same. Such as series connected resistor limits the current flowing through the light emitting diode (LED).


It is some time required to introduce electrical resistance in different circuit to limit the current through it. Resistor is an element of circuit which does the same. Such as series connected resistor limits the current flowing through the light emitting diode (LED).


In addition to that resistors serve many other purposes in electrical and electronic applications. The most essential requirement of a resistor is that its value of electrical resistance should not vary with temperature for a wide range. That means resistance variation with temperature must be as minimal as possible for a wide range of temperature. In other word the temperature coefficient of resistance of must be minimum for the materials by which a resistor is made of.


High Frequency Effects on Resistor

The effective resistance value of a resistor may be changed when it is subjected to alternating voltage. Not only that the value of resistance varies with variation of frequency of supply voltage. This change of resistance with frequency is called Boella effect. Actually it is not practically possible to make an ideal resistor. Practically it may have some inductor and capacitance in addition to its resistance. Therefore, the value of impedance of the resistor may vary with frequency. That is why a resistor is referred to be used within its useful frequency range. Useful frequency range is defined as the highest frequency limit beyond which the impedance of the resistor crosses its tolerance value.


High frequency effect on resistor depends upon its constructional feature. The impedance of wire wound resistor increases with frequency. On the other hand composition resistor reduces its impedance with increasing frequency. The impedance of film resistors does not change up to 100 MHz and then it decreases. Film resistors have the most stable high-frequency performance. The high frequency response of a resistor may also depend up to some extend on diameter of the resistor. It is seen that smaller diameter resistor has better frequency response. Because of that the length – diameter ration of high-frequency resistors is between 4:1 to 10:1.


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