May 2, 2014

Resistor



resistor

Definition of Resistor

A resistor offers resistance to the flow of electrical current. The resistance is that the live of opposition to the flow of current in a resistor. More resistance means that additional opposition to electrical phenomenon. The unit of resistance is ohm and represented as Ω. once one V electric potential is applied across a resistor and for that one ampere of current flows through it, the resistance of the resistor is alleged to be 1Ω;. Resistor is one among the foremost essential passive components in electrical and electronics engineering.

Resistor

Resistor is required minimum time to introduce resistivity in numerous circuits to limit the current through it. Resistor is a part of circuit which does the same. Like series connected resistor limits the electrical current flowing through the Light emitting diode (LED). Additionally to it resistors serve several alternative functions in electrical and electronic applications.


The most essential demand of a resistor is that its value of resistivity mustn't vary with temperature for a large varies. Meaning resistance variation with temperature should be as lowest as attainable for a large varies of temperature. In alternative word the temperature constant of resistance of should be minimum for the materials by that a resistor is formed of. 

Voltage Rating of Resistor

The voltage rating of a resistor is defined as the thoroughgoing voltage that can be applied through a resistor due to which power dissipation will be in its acceptable limit. In fact voltage rating of resistor is interrelated to the power rating. As we know that power rating of resistor is stated as:
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Where V is the functional voltage through the resistor and R is the resistance value of the resistor in ohms.

From the above equation it is clear that for restraining P, V must be limited for a specific resistor of resistance R. This V is voltage rating of resistor of power rating P watts and resistance R in Ω.

Power Rating of Resistor

As soon as current passes through a resistor there must be I2R loss. Therefore as per Joules law of heating there must be high temperature rise in the resistor. A resistor must be functioned surrounded by a temperature limit. So there should not be any damage to due high temperature. The power rating of a resistor is defined as the maximum power that a resistor can dissipate in the form of heat to preserve the temperature within maximum permissible limit. How much power a resistor will dissipate depends upon the material, sizes, voltage rating, maximum temperature limit of the resistor and ambient temperature.

Voltage Coefficient of Resistance

The resistance of a resistor may possibly also vary sometime with applied voltage across it. This modification is stated as a percentage of the resistance at 10% of rated voltage. Thus the voltage coefficient of resistance is given by
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Where R1 is the resistance at the rated voltage V1 and R2 is the resistance at 10% of rated voltage V2.


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