Between a thin and a thick copper wire of equal length, the resistance of the thin wire is higher. As we know, the heat generated in a conductor is proportional to the resistance of the conductor if the flow rate and flow time are constant. So, since the same current is being sent through both wires for the same period of time, the narrower wire has a higher resistance, so the heat generated in it will be higher. As a result, the thin will be hotter than that.
