A conductor is any material that allows electric charge to flow through it easily. The defining property is an abundance of charge carriers, typically electrons, that are free to move when a voltage is applied. But conductors have several other distinctive properties beyond just carrying current, from how they handle heat to how they behave in electric fields.
Why Electrons Move Freely in Conductors
In a metal like copper or silver, each atom gives up at least one of its outermost electrons. Those electrons detach from their host atoms and become shared across the entire material, while the atoms left behind become positively charged ions arranged in a fixed lattice. This creates what physicists sometimes call a “sea” of mobile electrons held together with the positive ions through metallic bonding.
From an energy perspective, conductors have a specific structure that sets them apart from insulators. Every solid has energy levels that electrons can occupy, grouped into bands. In a conductor, the band where electrons normally sit (the valence band) overlaps with the band where electrons need to be in order to move freely (the conduction band). Because there’s no gap between these two bands, at least some electrons can always move through the material. In insulators and semiconductors, a gap separates those bands, and electrons need a significant energy boost to cross it.
Low Electrical Resistance
The most obvious property of a conductor is low electrical resistance. Silver has the lowest resistivity of any metal at 1.59 × 10⁻⁸ ohm-meters, followed closely by copper at 1.68 × 10⁻⁸ ohm-meters. Copper is the standard benchmark for measuring conductivity in engineering. The International Annealed Copper Standard (IACS) defines high-purity annealed copper as 100% IACS, and other materials are rated as a percentage of that value. Silver comes in around 105% IACS, while aluminum, the next most conductive common metal, falls to roughly 61%.
Even though silver technically wins, copper dominates real-world wiring because it’s far cheaper and nearly as conductive. Aluminum is lighter still and commonly used in power transmission lines, where weight matters more than squeezing out every bit of conductivity.
How Temperature Changes Resistance
Conductor resistance isn’t fixed. It rises as temperature increases. When a metal gets hotter, the ions in its lattice vibrate more energetically. Those vibrations make it harder for electrons to travel through the material without colliding with something, which shortens the average distance an electron travels between collisions and increases resistance. This is why electrical components can perform differently on a hot day or after running for a long time.
Each metal has a specific temperature coefficient that describes how quickly its resistance climbs per degree. Copper’s coefficient is about 0.00386 per degree Celsius, and silver’s is similar at 0.0038. This positive temperature coefficient is a signature trait of metallic conductors. Semiconductors behave in the opposite way: their resistance drops as temperature rises because heat frees up additional charge carriers.
Conductors Also Conduct Heat
Good electrical conductors are almost always good thermal conductors, and this isn’t a coincidence. The same free electrons that carry electric current also carry thermal energy. When one end of a copper rod is heated, electrons in that region pick up kinetic energy and transfer it to neighboring regions as they move and collide. This relationship between thermal and electrical conductivity is formalized in the Wiedemann-Franz law, which states that the ratio of a metal’s thermal conductivity to its electrical conductivity is proportional to temperature. The proportionality constant is the same for virtually all metals, confirming that the same electrons are responsible for both types of conduction.
Electrostatic Behavior
Conductors have several unique properties when placed in static electric fields, and these matter for applications like shielding and grounding.
First, the electric field inside a perfect conductor is zero. Because charges are free to move, they redistribute themselves in response to any external field until they completely cancel it out internally. This is why a metal enclosure can shield sensitive electronics from outside electrical interference.
Second, any excess charge on a conductor sits entirely on its surface. Charges repel each other and spread as far apart as possible, which means they migrate outward. At the surface, the electric field points straight outward, perpendicular to the conductor. There is no component of the field running along the surface, because if there were, the free charges would keep moving until it disappeared.
Third, the entire conductor is at the same electric potential. Every point on and inside the conductor shares the same voltage. This equipotential property is a direct consequence of the zero internal field.
Not All Conductors Are Metals
Metals are the most familiar conductors, but they’re not the only ones. Electrolyte solutions, like saltwater or the liquid inside a battery, conduct electricity through the movement of ions rather than free electrons. In a lithium-ion battery, for example, the liquid electrolyte has an ionic conductivity around 10⁻² siemens per centimeter at room temperature. That’s lower than a metal but more than sufficient for the battery to function. Unlike metals, where only electrons carry current, in a liquid electrolyte both positive and negative ions contribute to conduction.
Graphite, plasma, and certain polymers also conduct electricity, each through different mechanisms. What they all share is the presence of mobile charge carriers, whether those are electrons, ions, or some combination.
Superconductivity: Zero Resistance
Certain materials lose all electrical resistance when cooled below a critical temperature. This state, called superconductivity, was first discovered in mercury cooled to roughly -452°F, just a few degrees above absolute zero. A current flowing through a superconductor will circulate indefinitely without any energy loss.
In the 1980s, researchers found a class of copper-oxide materials that become superconducting at much warmer temperatures, some above the boiling point of liquid nitrogen (-321°F). These high-temperature superconductors are still extremely cold by everyday standards, but liquid nitrogen is cheap and practical compared to liquid helium. Superconductors also expel magnetic fields entirely as they transition to their superconducting state, a property that enables technologies like magnetic levitation and ultra-powerful MRI magnets.
Key Properties at a Glance
- Free charge carriers: Metals have mobile electrons; electrolytes have mobile ions.
- Low resistivity: Silver leads at 1.59 × 10⁻⁸ ohm-meters, with copper close behind.
- Resistance increases with heat: Lattice vibrations impede electron flow at higher temperatures.
- Good thermal conductors: Free electrons transport heat and electricity simultaneously.
- Zero internal electric field: Charges redistribute to cancel any field inside the conductor.
- Surface charge only: Excess charge resides entirely on the conductor’s outer surface.
- Equipotential: Every point on a conductor in electrostatic equilibrium shares the same voltage.