T&M Understanding Resistivity: A Guide to Material Properties
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This article delves into the concept of resistivity and provides a handy table showcasing the resistivity values of various substances. We’ll explore what resistance and resistivity mean, and how they relate to the flow of electricity.
What is Resistance and Resistivity?
At its core, resistance is a material’s inherent ability to impede the flow of electrical current (or electrons). Think of it as friction for electricity.
The resistance of a wire, for instance, is affected by several factors. Consider a wire of length l and cross-sectional area a. Its resistance (R) can be calculated using the following equation:
Resistance (R) = ρ * l / a (Ohms)
Where:
- ρ (rho) = Resistivity of the material (measured in Ohm-meters)
- l = Length of the wire (in meters)
- a = Cross-sectional area of the wire (in square meters)
Several things influence a conductor’s resistance:
- Length: Longer wires have higher resistance.
- Cross-sectional area: Thicker wires have lower resistance.
- Type of material: Different materials offer different levels of resistance.
- Temperature: Resistance usually changes with temperature.
Resistivity, represented by ρ (rho), is an intrinsic property of a material. It describes how strongly that material resists electric current. Unlike resistance, which changes with size and shape, resistivity is a constant for a given material at a specific temperature.
Key points about resistivity:
- Resistivity changes with temperature.
- Good conductors of electricity have very low resistivity values.
- Good insulators have extremely high resistivity values.
Resistivity Table
The table below shows the resistivity values for various materials, measured in ohm-meters (Ω-m).
| Substance Name | Resistivity (Ω-m) |
|---|---|
| Aluminium | 2.65 x 10^-8^ |
| Brass | (0.6 to 0.9) x 10^-7^ |
| Cadmium | 6 x 10^-8^ |
| Cobalt | 5.6 x 10^-8^ |
| Copper | 1.7 x 10^-8^ |
| Constantan | 49 x 10^-8^ |
| Carbon (Graphite) | 3 to 60 x 10^-5^ |
| Gold | 2.4 x 10^-8^ |
| Germanium | 4.6 x 10^-1^ |
| Glass | 10^14^ |
| Iron | 1.0 x 10^-7^ |
| Lead | 1.9 x 10^-7^ |
| Manganin | 4.2 x 10^-7^ |
| Mercury | 98 x 10^-8^ |
| Nichrome | 1.1 x 10^-6^ |
| Nickel | 7 x 10^-8^ |
| Palladium | 1.0 x 10^-7^ |
| Platinum | 0.98 x 10^-7^ |
| Quartz | 7 x 10^17^ |
| Silver | 1.6 x 10^-8^ |
| Silicon | 6.4 x 10^2^ |
| Tungsten | 4.9 x 10^-8^ |
| Tantalum | 1.3 x 10^-7^ |
| Tin | 1.1 x 10^-7^ |
| Zinc | 5.5 x 10^-8^ |
