Resistance, Resistivity and Conductance, Conductivity and Temperature effect on Resistance
What is resistance?
Resistance means oppose, in electrical current - opposition that offers a substance to flow of electrical current.
It is denoted by 'Ω'
It is measured in ohm.
What is Conductance?
It can be defined as the reciprocal of Resistance.
It is denoted by G.
Resistivity (ρ)
Property of a material that indicates how much it will oppose flowing of current.
It is also called as Specific Resistance.
It is denoted by rho (ρ).
It depends on Resistance (R), Length (L) and Cross-sectional area of the conductor.
Resistance calculation
R - the resistance in ohms (Ω).
ρ - the resistivity in ohms-meter (Ω×m).
l - the length of the conductor in meter (m).
A -the cross-sectional area of the conductor in square meters (m2).
What is Conductivity?
It is defined as the reciprocal of Resistivity.
It is denoted by.
The best conductor is having the lowest value of specific resistance and similarly, the best insulator is having the highest value of specific resistance.
Factors affecting the value of Resistance.
1. Directly proportional to Resistivity of material (ρ)
2. Directly proportional to the length of conductor (L)
3. Inversely proportional to the cross-sectional area of the conductor (A).
4. Due to change in temperature of conductor will affects to the length of the conductor.
Effect of Temperature on Resistance or Relation of Resistance and Temperature
Effect of temperature on resistance of Pure Metals:
For pure metals temperature linearly (Rate of increase remains constant) increases with resistance.
The resistance of metal reduces with a reduction in temperature and it reduces to 0 Ω at -234.5˚ C.
How Resistance increases with temperature?
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Effect of temperature on resistance of Alloys:
Resistance for alloys increases with increase in Temperature but rate of change in resistance less than that of metals.
For some exception alloys such as Managing and Eureka the change in resistance with temperature is almost Zero.
Effect of temperature on resistance of Insulators:
Resistance for insulators decreases with increase in Temperature .
Hence materials at low temperature act as perfect Insulators and It will starts acts as good conductor at very high temperature .
Effect of temperature on resistance of Semiconductor:
The semiconductor material have a negative temperature coefficient of resistivity . Means Resistance for semiconductors decreases with increase in Temperature
Graphical Presentation for Temperature and Resistance relation
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