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When an electrical current flows through a wire, it encounters resistance, which is a property of the wire that results in the generation of heat due to the friction between the flowing electrons and the atoms of the wire. This phenomenon is described by Joule's law, which states that the power of heat generated is proportional to the square of the current and the resistance of the wire. As a result, the friction caused by the movement of charged particles within the conductor leads to an increase in temperature, which is often evident in the form of heat being produced.

In contrast, while options related to reduction in resistance, temperature decrease, or electrical expansion might sound plausible in different contexts, they do not accurately represent the dominant effect of electric current in an unmodified conductive wire under normal conditions. The key takeaway is that the flow of electrical current primarily results in heat generation as a direct consequence of resistance.