I am a physics teacher and demonstrated in the class that the voltage across at wall socket is around 220V ( in Europe )  and my student asked why we are connecting a voltmeter in series with power outlet ( I stated to my students previously that if we want to measure voltage of the resistor, we make a parallel connection with it.) I explained them that we need to think the power source as a battery and the internal resistance of new opened battery is very small compared to the internal resistance of the voltmeter.

He came out with the second question that the voltage drop across the voltmeter is not the same as voltage in the power source because there is internal resistance of power source of which we don't know. He claimed that the voltage across the power outlets needs to change depending the distance of wall outlet to the power plant. 

**My question is:** what is the internal resistance of the circuit coming from power plant to our home? Does it make too much difference?