My guesses follow the questions. -- Rich Michael Cook wrote: > > Hi guys. Just a few interesting questions for you here. Hopefully some > of you could tell me the answers! > > 1. Why are wall sockets (in the USA at least) 120 volts? Why not 12? Or > 150? Why not 12 volts? The resistive losses would be very high except for small lamps and motors. Why not 150 volts? I don't know the history of how motors and generators were built at the time but I would guess that they somewhat determined the voltage chosen. Maybe because it is the same as 10 12-volt batteries? Why 220 and 240 volts? I don't know those either. You didn't ask but... why 25, 50 or 60 Hz for the frequency? I have seen old motors and they have magnetic gaps that you can insert your fingers into. The voltages and frequencies are probably related as well. > 2. Why are most batteries 1.5 volts? Why not 1? This one is easy. The battery voltage is determined by the chemistry used in the battery. Carbon-zinc and alkaline cells are about 1.5 volts. Lithium cells are about 3 volts. Lead acid cells are about 2 volts. Most chips I use need > 5v, so why not 5? Or 2.5? I think this is because DTL and the derived TTL circuits need a few volts to work properly. At a much larger voltage they would waste power. 5 volts is a compromise. Older ECL and RTL used -5.2 volts and 3.6 volts respectivley. (Yes, ECL is older than TTL). More and more, both analog and digital are starting to use lower voltages such as 2.5 volts. Microprocessors use lower voltages to reduce power and current requirements. They can now -- and must -- work at these lower voltages because of the finer detail of their process dimensions. > 3. Why do computers use 12v and 5v instead of 15v and 5v, or some other > combination. They use 5 volts because computers are still based on TTL technology. (This is changing.) 12 volts is because a lot of circuits originally used 12 volt batteries. It is amazing how much inertia technology has. I, as well as Michael, would be interested in others' opinions and historical background on these questions. :-) > > Just some questions to ponder, thx. > > -Michael Cook > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body