how does a transformer work?
http://en.wikipedia.org/wiki/Transformer" [Broken] for an explanation of working and principles. In future, for complete explanation of concepts, start with your textbook or look for online resources.
Wow, sometimes Wickepedia gives really good explanations!
hey, thanks for the link. but i still have a doubt. for transmission of power, high voltages are used so as to reduce current in the wires. then power dissipation thru resistance would be i^2*R.but it can also be written as v^2/R. so what's the actual difference bwtn power supplied and power dissipated?
First thing you have to know is that P = v^2/r, where 'v' is voltage dropped across the resistive load. Internal resistances across a high voltage power line tend to be small compared to the main load, and hence voltage dropped across them is far smaller. This becomes even smaller with higher voltages. Therefore 'v' becomes small and hence power dissipated is low. Note that this 'v' is not the entire voltage of the power line, but merely a small fraction of it. This is called voltage division.
In the case of current however, no such division takes place in the power lines and in P=i^2r, 'i' actually stands for the total current in the lines. Thus the current has to be minimized to reduce loss.
the "R" in i2R losses in transmission lines is the resistance of the actual conductors that the current flows through. a v2/R should be more consisely called v2G losses and G would refer to the conductance between the conductors. i dunno what it's like around a high tension transmission line when it's raining or drizzling or misting or foggy (there might be some measurable inter-cable conductance or leakage, but when it's dry, that conductance, G, is pretty much 0. however, you have i2R losses all of the time, dry or not, because although air makes a pretty good insulator when it's dry, the conductivity of the cables is no better in dry weather than in wet.
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