Electrical conductivity is the measure of how well materials conduct electricity. All physical materials have the ability to conduct electricity, and those that have higher conductivity measures are called electrical conductors. Mostly the best electrical conductors are metals, in which closely linked atomic structures allow the free movement of electrons (or charges of electricity). This particular factor of electrical conductivity is not constant in nature, and varies within different conductors due to intrinsic and extrinsic factors. However, there are some generalised factors as well, which commonly affect the conductivity of conductors in a significant manner.
Variation in temperature of an electrical conducting material can change its conductivity. This variation occurs due to the thermal excitation of atoms within conducting materials, which is directly proportional to the increasing temperature. It means that increasing the temperature of an electrical conductor can interfere with conductivity. This effect is usually observed in different electrical devices and transmission lines, and for this reason, sensitive electronic devices are usually accompanied by cooling mechanisms that keep the conductor's temperature at a constant level.
Impurities refer to the presence of insulating particles of nonconducting elements within electrical conductors, resulting in decreasing the conductivity of these materials. These insulating substances are either present due to natural contamination, or because of manufacturing flaws. These impurities hinder the flow of current within conductors, which significantly decreases the conductivity levels.
Electromagnetic fields are present everywhere in the surrounding environment, and have their impacts on electrical conducting properties of conductors. Their presence with strong intensities and opposite polarities (alignments) often causes a change within the normal rate of current flow within electrical conductors. This effect is also known as magnetoresistance, since it contributes in varying resistance within electrical conductors through intense magnetic fields in the surrounding environment. Although electrical conductors also create electromagnetic fields when conducting current, these fields have their electrical and magnetic components aligned perpendicular to each other, so they're less of a problem for current flow. On the other hand, external electromagnetic fields are independent, and have the potential to interrupt the flow of current through these conductors.
Frequency of an electrical current is the number of oscillatory cycles it completes in a second, and is measured in hertz (Hz). This factor, when increased above a certain higher limit, causes electrical current to flow around a conductor instead of running through the conductor. This is called the skin effect, and usually happens when frequency of electrical current increases above 3 GHz (or 3,000,000,000 cycles per second), causing reduction in the electrical conducting properties of material. This effect is only observable in operations conducted with AC (alternating current), since DC (direct current) has an absolute frequency of 0 Hz and does not oscillate when it flow.