The reason given for the transmission of power by way of ac rather than by dc is that the ac voltage can be stepped up so that the current can be proportionately reduced. In that case the power loss is calculated by using the formula I^2 R. But my long standing doubt is how the resistance of the transmission cable wire is calculated? We know that the resistance of a wire increases with length. In that case, if the distance between the power plant and the receiving point, say a town, is 100 km, will not the resitance of a 100 km wire be extraordinasrily high? So, even if the current is very low, when the square of the current is multiplied by the resistance, will not the power loss increse with the increase in the distance? But, in all model calculations, resistance of the wire is kept constant. Certainly the quantity in the power formula is not the specific resistance but only the resistance. For a person well versed in this concept this question may be trivial in nature. But, I couldn't get a convincing explantion for the above doubt. Will any body thow light on this subject?