----- Original Message ----- From: "Michael Cook" To: Sent: Sunday, May 20, 2001 5:06 PM Subject: [OT]: Voltage Questions > 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? This is a tradeoff between safety (lower voltage) and efficiency (higher voltage) > 2. Why are most batteries 1.5 volts? Why not 1? Most chips I use need > 5v, so why not 5? Or 2.5? The voltage generated by a battery is determined by the specific chemical reaction involved. Different battery chemistries have different voltages. The old-fashioned Carbon-Zinc was 1.5V. Alkaline was also very close to 1.5V. NiCad and NiMH are actually about 1.2V. Some lithium based chemistries are about 3V per cell. Lead-acid (like in your car) is a bit over 2V. > 3. Why do computers use 12v and 5v instead of 15v and 5v, or some other > combination. 5V because the traditional voltage for logic chips in the early days of digital logic. 12V is a reasonable choice for driving the motors in disk drives. > 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 hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu