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Actually, the BJT is a positive temperature coefficient device. As they get warm, hFe increases, causing more current flow. This can lead to thermal runaway. That is why most class A common emitter configurations use an emitter resistor to place limits on the hFe demand, eliminating thermal drift and runaway.

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Because if temperature of semiconductors is increased then number of free electrons per unit volume increases its conductivity increases and resistivity decreases.

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Because as they get colder their resistance increases and vise versa.

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Q: Why semiconductor has negative temperature coefficient of resistance?
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Continue Learning about Electrical Engineering

What is the Tempetature coefficient of an extrinsic semiconductor?

negative


What happens when the temperature of a forward biased diode is increased?

What happens depends on the temperature coefficient of the diode. If that diode has a positive temperature coefficient, it resistance increases with increased temperature. A diode with a negative temperature coefficient does the opposite.


Do The resistance of a material generally increases as its temperature increases?

The answer to this depends on the material from which the resistance is made. For most materials resistance increases with increasing temperature. This is referred to as having a "positive temperature coefficient". Some materials have a negative temperature coefficient; these do have uses in electronics.


What is the mathematical relationship between resistance and conductance?

The relationship between resistance and temperature is determined by a material's temperature coefficient of resistance (symbol, the Greek letter 'alpha'). In general, pure metal conductors are said to have a positive temperature coefficient of resistance, which means that their resistance increases with increase in temperature; in general, insulators have a negative temperature of resistance, which means their resistance decreases with an increase in temperature. Carbon, a conductor, also has a negative temperature coefficient of resistance. This negative temperature coefficient of resistance explains why insulators fail at higher temperatures.This topic is relatively complicated, so just one example will be given. Assuming we know the resistance (R0) of a material at 0oC , then we can find its resistance (Rx) at another temperature (Tx), using the following equation:Rx = R0 (1 + alpha Tx)


What Materials have a negative temperature coefficient?

Glass, Ceramics, Semiconductors

Related questions

Why does the resistance of a semiconducting material decrease when the temperature increases?

The no of electrons in the conduction band increases when the temperature of the semiconductor material increases. therefore resistance decreases. This is also know as "Negative temperature coefficient"


What is the difference between positive and negative temperature coefficient of resistance?

Negative temperature coefficient of resistance means that as the temperature of a piece of wire or a strip of semiconducting material increases, the electrical resistance of that material decreases.


Why do the semiconductors have negative temperature coefficient whereas the metals have positive values?

Semiconductors: When temperature increases, more electrons jump to conduction band from valance bond. Hence resistance decreases. Metals: Already plenty of electrons are there in conduction band. When temperature increases, the electrons in conduction band of metal vibrate and collide each other during their journey. Hence the the resistance of metal increases with increase of temperature. S.Lakshminarayana


What is the relationship between resistance and temperature?

• ntc 'negative temperature coefficient': its resistance decreases as the temperature increases• ptc 'positive temperature coefficient': its resistance increases as the temperature increases


Why does the resistance of a thermistor decrease as the temperature rises?

Some materials have negative temperature coefficients of resistance, and some have positive temperature coefficients. Carbon is an example of a substance with a negative thermal coefficient of resistance, so it's resistance will decrease as it gets hotter.


If a carbon resistor increases in temperature its resistance will?

This depends on the type of conductor. If the conductor has a positive coefficient the resistance will increase. If the conductor has a negative temperature coefficient the resistance will decrease.


How the resistance of conducting material vary with temperature?

Well, there's typically two types of materials-Those with positive temperature coefficient and those with negative temperature coefficient. Positive temperature coefficient are those whose resistance increases as temperature increases. Negative temperature cofficient are those whose resistance decrease when the temperature increase. There are however some alloys such as Manganin& Constantan whose resistance is not affected by temperature


Does carbon have a nearly zero temperature coefficient of resistance?

Yes, carbon has a negative temperature coefficient. -0.5*10^3/C


What is the Tempetature coefficient of an extrinsic semiconductor?

negative


What is the difference between PTC and NTC resistors?

positive temperature coefficient vs. negative temperature coefficient resistance increases or decreases with increase of temperature, respectively.


What happens when the temperature of a forward biased diode is increased?

What happens depends on the temperature coefficient of the diode. If that diode has a positive temperature coefficient, it resistance increases with increased temperature. A diode with a negative temperature coefficient does the opposite.


Why does the resistance of a thermistor change when you change its temperature?

The resistance of a thermistor changes when its temperature changes due to the inherent properties of the thermistor material. In a negative temperature coefficient (NTC) thermistor, the resistance decreases as the temperature increases, whereas in a positive temperature coefficient (PTC) thermistor, the resistance increases as the temperature rises. This change in resistance is caused by the variation in the number of charge carriers (electrons or holes) and their mobility within the material as temperature changes.