- Electrical Properties Definition: Electrical properties of materials are characteristics that determine how suitable a material is for electrical engineering applications.
- Resistivity: Resistivity is the property of a material that resists electric current flow. It is the inverse of conductivity.
- Conductivity: Conductivity is how easily electric current flows through a material. It’s the opposite of resistivity.
- Dielectric Strength: Dielectric strength measures how well a material can withstand high voltages without breaking down.
- Temperature Coefficient of Resistance: This coefficient shows how a material’s resistance changes with temperature, impacting its performance in different conditions.
Electrical properties describe how a material conducts current, stores electrical energy and responds to electric fields or temperature differences. They guide material selection for Electrical Engineering applications. Permittivity describes a material’s polarization response to an electric field, while the other main Electrical properties of engineering materials are listed below.
- Resistivity
- Conductivity
- Temperature coefficient of Resistance
- Permittivity
- Thermoelectricity
Resistivity
Resistivity, denoted by ρ, measures how strongly a material opposes electric current. For an isotropic material under stated conditions, it is the reciprocal of conductivity.
For a uniform specimen, Resistivity is ρ = RA/l, where the dimensions describe the tested conductor.
Here, R is the measured resistance in ohms (Ω).
A is the cross-sectional area of the conductor in m2.
The length l is measured in metres, and the SI unit of resistivity is the ohm metre (Ω m). The following values are approximate reference values. Purity, alloying, microstructure, temperature and direction can change the result.
| Sl. No. | Element | Approximate resistivity at 20oC in Ω m |
| 1 | Silver | 1.59 × 10-8 |
| 2 | Copper | 1.7 × 10-8 |
| 3 | Gold | 2.44 × 10-8 |
| 4 | Aluminum | 2.82 × 10-8 |
| 5 | Tungsten | 5.6 × 10-8 |
| 6 | Iron | 1.0 × 10-7 |
| 7 | Platinum | 1.1 × 10-7 |
| 8 | Lead | 2.2 × 10-7 |
| 9 | Manganin | 4.82 × 10-7 |
| 10 | Constantan | 4.9 × 10-7 |
| 11 | Mercury | 9.8 × 10-7 |
| 12 | Carbon (Graphite) | 3.5 × 10-5 |
| 13 | Germanium | 4.6 × 10-1 |
| 14 | Silicon | 6.4 × 102 |
| 15 | Glass | 1010 to 1014 |
| 16 | Quartz (fused) | 7.5 × 1017 |
Conductivity
Conductivity, denoted by σ, measures a material’s ability to carry electric current. For the same conditions used to state resistivity, Conductivity of material is σ = 1/ρ. Conductivity varies with temperature, composition and material condition, so a quoted value needs those conditions.
Its SI unit is the siemens per metre (S/m), equivalent to 1/(Ω m). Mho is an obsolete name for the siemens.
Dielectric Strength
Dielectric strength states the electric-field magnitude at which breakdown occurs under a specified test. This test result is commonly reported for an insulating material and differs from a safe continuous operating voltage. Electrode shape, gap, material thickness, waveform, frequency, temperature, moisture, defects and test duration can change the result. The values below are illustrative only and must not replace grade-specific test data or insulation-coordination requirements.
| Sl. No. | Material | Illustrative dielectric strength [kV/cm] |
| 1 | Air | 30 |
| 2 | Porcelain | 80 |
| 3 | Paraffin Wax | 120 |
| 4 | Transformer oil | 160 |
| 5 | Bakelite | 220 |
| 6 | Rubber | 280 |
| 7 | Paper | 500 |
| 8 | Teflon | 600 |
| 9 | Glass | 1200 |
| 10 | Mica | 2000 |
Temperature Coefficient of Resistance
The temperature coefficient of resistance states the fractional resistance change per degree at a defined reference temperature. A linear coefficient is an approximation over a suitable temperature range.
For the linear model, the resistance change depends on the initial resistance, the temperature change and the material’s coefficient.
- R2 – R1 ∝ R1
- R2 – R1 ∝ t2 – t1
- The coefficient and valid range depend on the conductor material and condition.
Here, R1 is the resistance at reference temperature t1oC, and R2 is the resistance at temperature t2oC.
The proportional relationship is R2 – R1 ∝ R1 (t2 – t1).
For a constant linear coefficient, R2 – R1 = α1 R1 (t2 – t1), so R2 = R1 [1 + α1 (t2 – t1)].
In this expression, α1 is the temperature coefficient of resistance at t1oC. Its unit is reciprocal degrees Celsius (/ oC) or reciprocal kelvins. The coefficient itself can vary with temperature, purity and material condition, so the table contains approximate reference values.
| Sl. No. | Element | Approximate coefficient at the stated reference temperature in /oC |
| 1 | Manganin | 0.00002 |
| 2 | Constantan | 0.00017 |
| 3 | Nichrome | 0.0004 |
| 4 | Mercury | 0.0009 |
| 5 | Silver | 0.0038 |
| 6 | Copper | 0.00393 |
| 7 | Annealed copper | 0.00393 |
| 8 | Platinum | 0.003927 |
| 9 | Aluminum | 0.00429 |
| 10 | Carbon (Graphite) | – 0.0005 |
| 11 | Germanium | – 0.05 |
| 12 | Silicon | – 0.07 |
Thermoelectricity
The Seebeck effect produces an electromotive force in a circuit made from dissimilar conductors when their junctions are at different temperatures. This effect is the basis for thermocouples and temperature-based transducers. The voltage depends on the conductor pair and both junction temperatures, so practical temperature measurement needs a known reference-junction temperature or electronic compensation.
