Four different things affect the overall resistance of a wire: the material, the length, the cross-sectional area, and the temperature. resistance is directly proportional to length and inversely proportional to cross sectional area.
Resistivity can be used to describe the electrical property of a material (resistance only describes the electrical property of a single component). E.g copper wires may have a different resistance (e.g if they are different lengths) but overall copper has a unique resistivity. We can use the above facts (that resistance is directly proportional to length and inversely proportional to cross sectional area) to make an equation with resistivity as the constant:
Resistivity has the symbol pho (ρ) and the unit ohm meter (Ωm). Resistivity is defined as the product of the resistance of a component made of the material and it's cross sectional area, divided by it's length.
A bit of a mouthful if you ask me.
Like resistance, resistivity also varies with temperature.
How would we determine the resistivity of a material?...
Investigate how the resistance of a wire varies with length. Measure values of potential difference across varying lengths of wire. Use V=IR to determine R. A graph of R against L will give a gradient of ρ/A. Multiply the gradient by A and you have ρ, the resistivity.
Good conductors have a very small resistivity whilst insulators have a very large resistivity.
In this section we also need to know about NTCs and the variance of resistance with temperature of a thermistor. I have put this information in this section.
Resistivity can be used to describe the electrical property of a material (resistance only describes the electrical property of a single component). E.g copper wires may have a different resistance (e.g if they are different lengths) but overall copper has a unique resistivity. We can use the above facts (that resistance is directly proportional to length and inversely proportional to cross sectional area) to make an equation with resistivity as the constant:
R = (ρL)/A
Resistivity has the symbol pho (ρ) and the unit ohm meter (Ωm). Resistivity is defined as the product of the resistance of a component made of the material and it's cross sectional area, divided by it's length.
A bit of a mouthful if you ask me.
Like resistance, resistivity also varies with temperature.
How would we determine the resistivity of a material?...
Investigate how the resistance of a wire varies with length. Measure values of potential difference across varying lengths of wire. Use V=IR to determine R. A graph of R against L will give a gradient of ρ/A. Multiply the gradient by A and you have ρ, the resistivity.
Good conductors have a very small resistivity whilst insulators have a very large resistivity.
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