Electrical conductivity, or conduction, describes the amount of current that will flow through a given material when an electric field is applied to it. Electrical conductivity, represented by the symbol σ, can be directly related to the electrical resistivity, or resistivity, of the material, represented by the symbol ρ by the equation σ = 1/ρ.
Electrical conductivity is defined as the ratio of the current density to the electric field strength and can be expressed as
σ = J / E (1)
where
σ = electrical conductivity (1/ohms m, 1/Ω m, siemens/m, S/m, mho/m)
J = current density (amps/m2)
E = electric field strength (volts/m)
One siemens - S - is equal to the reciprocal of one ohm and is also referred to as one mho.
Here are some basic values of electrical conductivity for various materials.
Electrical conductivity units
Conductivity is a term used in physics to describe how well a substance transmits an electric current. Specific resistances are often measured in ohms (m) or micro-ohms per centimeter (cm). The units pascal second/meter (Pa s/m) and pascal second/meter (Pa s/m) are also used. A conductor is an electrically low-resistance substance. Because most metals have mobile electrons that may move when an electric field is applied to them, such as in a wire, they have a high conductivity. In contrast, some insulators, such as most polymers and glass, have a high resistivity because their crystal structure prevents any electrical current from passing through them.
Electrical Conduction in Solids
Solid materials, such as metals and semiconductors, are good conductor of electricity. Electrons migrate from one atom to another within a substance during electrical conduction. Atoms establish covalent bonds, which may be thought of as two atoms sharing one or more electrons. Conductive materials give away electrons in this way, allowing current to flow. The capacity to transmit electrons is the most significant aspect in determining how efficiently a substance conducts electricity. Other parameters, like as atomic structure and size, do, nevertheless, have a role.
Electrical Conduction in Liquids
Because liquids are typically made up of randomly moving molecules, they usually don’t conduct electricity very well. However, when liquids contain particles that can easily move from one molecule to another, they become more conductive. Water is a good example. It contains positively charged ions (i.e., hydroxide ions) that allow it to conduct electricity very well. In general, electrical conductivity increases as you go down columns in a periodic table (for elements with more than one electron per atom). For example, lithium and sodium are both much better conductors than oxygen or nitrogen because their atoms have fewer electrons per atom and thus more loose electrons for conducting electricity.
Electrical Conduction in Gases
All gases conduct electricity to some degree. But some are better than others. To be an effective insulator or semiconductor, a material must have an electrical resistance in excess of 100 billion ohms per meter (100 GΩ·m). If a material has a resistance below 1 Ω·m, it can carry a substantial current and make a good conductor. Some gases have such low resistances that they can pass significant amounts of current even at room temperature. The gas most often used for refrigeration is ammonia, which has electrical conductivity about nine times that of air. About 75% of all commercial cooling applications rely on ammonia’s ability to rapidly transport heat away from machines and other equipment.
Electrical Conduction in plasma
In Earth's atmosphere, these layers are made of oxygen and nitrogen. The molecules in these layers are electrically charged and can thus be ionized by energy from sunlight or weather conditions. The charged molecules create a plasma which is the fourth state of matter after solid, liquid, and gas states. This electrified layer that surrounds our planet gives off an electric field that acts as a shield to protect life on Earth from space radiation such as cosmic rays. It also helps with radio communication signals for GPS (Global Positioning System) navigation devices by deflecting them back to satellites located between .7 miles to 12 miles above Earth's surface.
Plasma also conducts electricity. In fact, most gases are excellent electrical conductors because they are made up of charged particles (atoms and electrons). The first use for plasma was in fluorescent lamps in 1923. Scientists combined mercury with a metal called argon to create ionized gas or plasma. Then they sent an electric current through it, causing it to glow. You can see how excited everyone got about using plasma: It’s cheap, it works on high voltages and has a very long lifespan if left untouched. Plasma TVs were invented in 1993! They quickly became all-the-rage among consumers because they produced sharper images than standard televisions; television manufacturers couldn’t keep up with demand.
Electronic Devices, Resistance and Resistors
At its most basic, a resistor is an electronic device that resists or obstructs the flow of electricity. It's made up of thin wire in an intimate circuit with another component, such as a capacitor or an inductor. When current passes through these components, they generate heat. Although resistors aren't dangerous to touch and don't contain any toxic materials, they're fragile devices that have certain elements you need to understand before working with them. A quick primer on electrical conductivity can go a long way toward making sure your resistors work when you want them to and last for years.
Electrical Conduction in Living Organisms
Electrical conduction is necessary for life. Everything from heartbeats to neuron firings to muscle contractions relies on electricity, and it’s facilitated by cells that specialize in transporting electrical charges. In nerve cells (neurons), these are known as sodium-potassium pumps, which carry electrically charged particles in and out of a cell, keeping its voltage just slightly positive with respect to its surroundings. And it’s true that many other types of cells have these channels as well—but they aren’t necessarily used for carrying ions. For example, muscles use calcium channels for contraction, which is really just a way to keep them from relaxing after every single beat.
Importance of electrical conductivity
Electrical conductivity is one of those properties that a lot of people use, but few people stop to think about what it actually means. For example, how many times have you pulled a fork out of a pot and then burned your tongue on hot food? That’s because foods have different electrical conductivities. Silverware handles are almost always made from silver or aluminum, both metals with low electrical conductivities. Food on forks will heat up more quickly in contact with silver or aluminum than it will in contact with other materials like plastic or stainless steel that have high electrical conductivities. Your tongue feels heat transfer faster in metal versus plastic, so you can avoid burning your mouth if you know whether your silverware is made from silver, aluminum, or some other material.
Conclusion
Electrical conductivity is often a metric that is used to describe how easily a material can transmit electricity. For example, water will not easily transmit electricity while gold will, meaning that gold has higher electrical conductivity than water. A material’s electrical conductivity will change with temperature and pressure as well. And while some materials have high electrical conductivities (such as gold and silver), they are rarely used because they also corrode quickly in moist environments, making them not-so-great for building things like wires. The most common conductor used today is copper, which has a low cost and good electrical conductivity. Copper was discovered by humans around 10,000 years ago but it wasn’t until 1786 that scientists found out that it could be drawn into wire. The discovery led to what we now know as wireless communication – or more commonly known as telephones!
