I have seen when a resistor is connected to a battery, it carries the same voltage across the resistor, if the resistance is changed the current changes but voltage remains the same making the battery drain out fast as it has a certain amount of stored energy and if current increases it drains fast that is it sends more energy per unit time,

but in power station ac supply keeping the power same we change the voltage where as it should remain constant as in a battery only we can change resistance and there by current,

not getting this clarity, pl clarify,

  • $\begingroup$ Re, "if the resistance is changed the current changes but voltage remains the same." That is because of how batteries work, and it is a sufficiently important idea in electronics design that it has a special name: A battery is a fairly good approximation of an ideal voltage source, and the power line supplying your home is a very good approximation of an ideal AC voltage source. $\endgroup$ Feb 22, 2020 at 19:54

1 Answer 1


A power station sees two sources of resistance. The consumer: As he switches on more devices (in parallel) he presents less resistance and draws more power. And The power lines: Power lost to the resistance of the power lines is proportional to the square of the current. The power being delivered by the line is voltage times current. If you can increase the voltage, then less current is required. Transformers are used to step up the voltage that goes into the lines. The long lines run at a very high voltage. In your neighborhood, and then on your street the voltages are stepped back down. If you have overhead lines, you can see the transformers on some of the poles.

  • $\begingroup$ while using tranformers if voltage is increased,will not current decrease and vice versa,thanks. $\endgroup$
    – sachin
    Feb 23, 2020 at 10:20
  • $\begingroup$ That's the point. You want less current in the long power lines, but the consumers still determine how much current is drawn at a relatively low voltage. That in turn determines the current at a high voltage. $\endgroup$
    – R.W. Bird
    Feb 24, 2020 at 14:35
  • $\begingroup$ thanks,my main concern is how the power line sends at high voltage when the voltage changes sinusoidally every moment,more over according to ohm's law if potential is high,current should increase what is not the case here. $\endgroup$
    – sachin
    Feb 24, 2020 at 14:51
  • $\begingroup$ An AC voltmeter generally reports the rms (root mean square) value of a sinusoidal voltage. (For a higer voltage, the peaks of the sine wave get higher.) $\endgroup$
    – R.W. Bird
    Feb 24, 2020 at 19:42
  • $\begingroup$ thanks,is it like the power and voltage are constant in the generating station and when it says it send power at high voltages,the voltage is increased only by the use of a transformer. $\endgroup$
    – sachin
    Feb 25, 2020 at 11:05

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