The flow of electrical current depends upon the movement of charge carriers, typically electrons, through a material. Resistance measures a material’s opposition to this flow, and temperature represents the average kinetic energy of its particles. These three concepts are linked, but their relationship changes depending on the material’s composition. Understanding this interplay requires defining how thermal energy influences the subatomic structure of a substance. Increasing heat can either impede or enhance the ability of a material to conduct electricity.
The Underlying Physics of Thermal Influence
Thermal energy introduced into a solid material is absorbed by its constituent atoms, causing them to vibrate with greater intensity. These atoms are fixed in a regular arrangement known as a crystal lattice. As the temperature rises, the amplitude of this atomic vibration increases, which directly impacts the path of moving charge carriers.
The flowing electrons must navigate the spaces between these vibrating atomic cores. Increased thermal vibration causes more frequent and energetic collisions, a process known as scattering. This scattering impedes the directed movement of the electrons, lowering their average drift velocity through the material.
This physical mechanism—where thermal energy leads to increased lattice vibration and greater electron scattering—always hinders the flow of charge. The final outcome on electrical current is determined by whether the material’s properties are dominated by this scattering effect or by the generation of new charge carriers.
Temperature Effects in Conductors
Metallic conductors, such as copper and silver, possess a vast number of free electrons that are only loosely bound to their parent atoms. These materials have an extremely high density of charge carriers readily available for current flow. Because of this abundance, the generation of new carriers by thermal energy is negligible compared to the existing population.
When a conductor’s temperature rises, the dominant effect is the increased scattering caused by the vigorous vibration of the crystal lattice atoms. The existing free electrons collide more often with these thermally excited atoms, increasing the material’s resistance. This increase in resistance directly leads to a decrease in the electrical current, assuming the applied voltage remains constant.
Conductors exhibit a Positive Temperature Coefficient (PTC) of resistance. This means that as temperature increases, the electrical resistance of the material increases predictably. This principle is important for engineers, who must factor in the resistance increase in power transmission lines during hot weather, as the higher resistance leads to greater energy loss.
Temperature Effects in Semiconductors
Semiconductors, such as silicon and germanium, exhibit a radically different response to rising temperatures compared to conductors. At room temperature, these materials have significantly fewer free charge carriers because their valence electrons are tightly held within fixed, stable structures called covalent bonds. Consequently, their electrical resistance is initially much higher than that of metals.
When thermal energy is applied to a semiconductor, the energy can become sufficient to break these covalent bonds, releasing a large number of electrons that become new, mobile charge carriers. Each broken bond creates both a free electron and a positively charged vacancy, known as a hole, effectively generating a pair of carriers available for conduction.
While increased temperature still causes atomic lattice scattering, the vast increase in the number of available charge carriers is the overpowering factor in semiconductors. The massive influx of new electrons and holes dramatically increases the material’s conductivity, leading to a net decrease in its electrical resistance.
This contrasting behavior means that semiconductors exhibit a Negative Temperature Coefficient (NTC) of resistance. As the temperature rises, the resistance drops, and the electrical current increases. This unique property is fundamental to the operation of modern electronic devices, including transistors and temperature-sensing devices called thermistors, which rely on this predictable change in resistance with temperature.