Question

Resistance and its dependence​

Answer 1

Answer:

There are three basic measurements which can be made in an electrical circuit. Voltage and current are the first two, and the third is resistance.

As electrical resistance is such a basic concept in electrical and electronic circuits it is necessary to answer some questions: what is resistance, what are resistors, and how resistance affects circuits.

Temperature Dependence of Resistivity

Based on the conductivity of the materials, they are classified into three – conductors, semiconductors and insulators. Conductorshave low resistivities ranging from 10-8Ωm to 10-6 Ω m while insulators have high resistivities which can be 1018 times greater than metals. Resistivity is indirectly proportional to the temperature. In other words, as you increase the temperature of  materials, their resistivities will decrease. But this is not true for every material i.e.,all materials do not have same dependence on temperature.

The resistivities of metallic conductors within a limited range of temperature is given by the following equation:

ρT= ρ0 [1 + a(T–T0)]

Here,

ρT= resistivity at a temperature T

ρ0 =resistivity at a reference temperature T0

a= temperature coefficient of resistivity; the dimension of a is (Temperature)-1

According to the above equation, a graph of ρTplotted against T would be a straight line i.e., the resistivity of a metallic conductor increases with increasing temperature.

As we mentioned, different materials have a different dependence on temperature. For example, materials like Nichrome, Manganin and constantan are less likely to change their resistivities with temperature. Hence, they are employed in wire bound standard resistors. However, semiconductors exhibit an indirect relation with temperature. Resistivities of semiconductors decrease with increasing temperatures.

In terms of ‘n’

We know resistivity, ρ is given by

ρ= 1/σ = m/ne2ζ

Here, n (no. of free electrons) and ζ (the average time between collisions) are inversely proportional to ρ.

In metals, ‘n’ does not change with temperature. However, the increase in temperature can increase the collision of electrons. This reduces the ζ and implies that increase in temperature increases the ρ. However in insulators and semiconductors, ‘n’ increases with the increasing temperature. Thus an increase in temperature decreases the ‘ρ’ in them.

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Answer 2

HeRe Is Your Ans ⤵

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➡Resistance Is The Property Of a Conductor which Resist Current

➡The SI Unit Of resistance Is Ohm

Factors On Which Resistance Of a Conductor Depends :-

# Length Of The Conductor

# Area Of Cross Sectional Of The Conductor

# Nature Of The Material

# Temperature

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