ANSWER: Why use AC?

RP

Why use AC

First reason of supplying AC to houses is historic. When Edison's company was sending electricity to houses in beginning, it was all DC. Later machines were produced that could produce electricity in much more efficient way and suppy at cheaper cost. Reason was obvious - Edison's rivals could use turbines to produce power with utmost ease and they could transmit power exteremly efficiently as AC uses sine waves.

Starting from that, transformers, stepping up and down of power became possible with AC, reducing the losses even further. Then there are other inherent advantages of AC such as you dont un-necessarily charge something up if a power cable is falling on something, there are ways to reduces losses in AC even further that are not at all there in DC and so on.
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What really is a funny quiz question perhaps is - Current is defined as
"Charge flowing through a conductor" in +2 physics books. Now in AC, typically an electron in power transmission wire moves merely 10 atoms far to a direction when it is called back to oscillate again back and forth.
So question is if this electron never reached the bulb in my house, how come it glows?


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Roger
Why use AC? ..flashback

Mr. Edison, the inventor of the light bulb, strongly promoted DC (Direct Current) and was strictly against AC (Alternating Current). AC was invented by Nikola Tesla. AC was more economical to distribute over large distances as it had lesser distribution losses. The AC popularity fast caught up and hence it is used everywhere today.

However the trains in Mumbai still operate on DC (1500V). The railway ministry has realised that significant power is wasted and so has decided to use AC for trains. Disadvantage is that people traveling on rooftops will be electrocuted if AC is used, even if they are upto 2 meters away from the cable. Any idea why?

Roger
AC funny question + answer

This is in reply to RP's funny question.......nobody answered it till now. let me answer it :-).
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Q) What really is a funny quiz question perhaps is - Current is defined as "Charge flowing through a conductor" in +2 physics books. Now in AC, typically an electron in power transmission wire moves merely 10 atoms far to a direction when it is called back to oscillate again back and forth.
So question is if this electron never reached the bulb in my house, how come it glows?

Ans) Imagine there is a long pipe (the wire) that is completely filled with water (the electrons). Now what will happen if i push the water a little from one end of the pipe. The water on the other end of the pipe will immediately push forward. The reverse happens when i pull back the water. So even though the water molecules at one end of the pipe have not reached the other end, the molecules at the other end have moved back and forth. Thus energy transfer has taken place (i.e. moving of water molecules). I could use this energy to do some work, (e.g. turn a propeller).

This can also answer the 2nd funny question below
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Q) In case of Direct current, electrons move in a copper conductor at a speed of only 1/4mm per second. For such a slow speed it will take an electron several minutes to travel a few inches of wire between the battery and the bulb. How come then does the light bulb turn on instantaneously?


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RP
Funny question - serious answer

Many a times funny questions pose fundamental aspect to be answered and people just dont answer it. Thanks for bringing it up Roger. What I wanted to promote was that every one around "teaches" current wrongly as when charge passes through a conductor. Where as it should be defined as charge passing through a plane in space. Then all things fall right in place.

Thanks for coming in to answer. Water hose analogy is really good in teaching simple, yet relevant concept. In 12th/13th chapter in Resnick-Halliday-Walker the chapter that described current in +2 (excuse me I have long forgot the chapters now :) long time) that was the only book I found that explained it correctly.