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Why can metals conduct both electricity and heat?
In everyday life, we all know that metals are strong conductors of electricity and heat. However, these two phenomena actually share a common physical nature—both are related to electrons.
1. Conductivity
In the absence of an external electric field, the free electrons in a metal are constantly moving, but their directions are chaotic, and overall they cancel each other out, resulting in no current.
Once a voltage is applied, the electrons are acted upon by the electric field and begin to move in a direction opposite to the field, thus generating a current.
However, as these electrons move, they collide with positive ions in the metal lattice, transferring the energy they gain to the ions, causing the metal conductor to heat up (this is known as "resistive heating").
2. The Relationship between Resistivity and Temperature
The electrical conductivity of a metal depends on its resistivity. For most metals, as the temperature rises, their resistivity also increases, causing their electrical conductivity to decrease.
This is why overheating can affect the efficiency of electrical wiring.
3. Thermal Conductivity
The ability of metals to conduct heat is also due to the presence of free electrons.
In high-temperature regions, free electrons gain more kinetic energy, which they then carry to lower-temperature regions through their movement, achieving energy transfer.
In other words, electrons act like "porters," continuously moving heat energy from the hot end to the cold end. This is why metals generally have excellent thermal conductivity.
Summary
Both electrical and thermal conductivity are essentially the result of the "electron gas": the density and motion of electrons determine the electrical and thermal properties of metals.
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