- 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.
To choose the right material for an engineering product, we need to understand the electrical properties of materials. These properties determine if a material is suitable for specific Electrical Engineering applications. Some of the typical Electrical properties of engineering materials are listed below-
- Resistivity
- Conductivity
- Temperature coefficient of Resistance
- Permittivity
- Thermoelectricity
Resistivity
Resistivity is the property of a material that resists the flow of electric current. It is the inverse of conductivity.
It is dented by ‘ρ’. Resistivity of a material of a conductor can be determined as below
Where, ‘R’ is the resistance of conductor in Ω.
‘A’ is the cross sectional area of conductor in m2
‘l’ is the length of the conductor in meter SI unit of resistivity of is Ω¦-meter. Resistivity of some materials is listed below
| Sl. No. | Element | 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
It is the property of material with allow the flow of electric current through material. It is a parameter which indicates that how easily electric current can flow through the material. It is denoted by ‘σ’. Conductivity of material is the reciprocal of resistivity. Conductivity of material can be determined by,
Its SI unit is 1/(Ω-meter) or ℧/meter.
Dielectric Strength
It is the property of material which indicates the ability of material to withstand at high voltages. Generally it is specified for insulating material to represent their operating voltage. A material having high dielectric strength can withstand at high voltages. Generally, it is represented in the unit of KV/cm. Dielectric strength of some insulating materials are listed below-
| Sl. No. | Material | Dielectric Strength [KV(max.)/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 of a material indicates the change in resistance of material with change in temperature. Resistance of conductor changes with change of temperature.
The rise in resistance of a material with rise in temperature depends on following things,
- R2 – R1 ∝ R1
- R2 – R1 ∝ t2 – t1
- Property of material of conductor.
Where, R1 is the resistance of conductor at temperature of t1oC and R2 is the resistance of conductor at temperature of t2oC.
Hence, from above, R2 – R1 ∝ R1 (t2 – t1)
Or, R2 – R1 = α1 R1 (t2 – t1) ⇒ R2 = R1 [1 + α1 (t2 – t1)]
Where, α1 is temperature coefficient of resistance of material at temperature of t1oC. Its unit is /oC. Temperature coefficient of resistance of material is also depends on temperature. emperature coefficient of some materials are listed below,
| Sl. No. | Element | Temperature Coefficient of Resistance in /oC |
| 1 | Manganin | 0.00002 |
| 2 | Constantan | 0.00017 |
| 3 | Nichrome | 0.0004 |
| 4 | Mercury | 0.0009 |
| 5 | Silver | 0.0038 |
| 6 | Copper | 0.00386 |
| 7 | Annealed copper | 0.000393 |
| 8 | Platinum | 0.003927 |
| 9 | Aluminum | 0.00429 |
| 10 | Carbon (Graphite) | – 0.0005 |
| 11 | Germanium | – 0.05 |
| 12 | Silicon | – 0.07 |
Thermoelectricity
When the junction of two different metals is heated, it produces a small voltage, called thermoelectricity or the thermoelectric effect. This effect is the basis for thermocouples and some temperature based transducers. It can be used to generate electricity and measure temperature changes.
