Physics Help Forum A 12 V battery...

 Feb 26th 2009, 08:24 PM #1 Junior Member   Join Date: Feb 2009 Posts: 2 A 12 V battery... A 12 V battery sends a charge of 84 Ah through a circuit. a) How many coulombs of charge does this represent b) If the charge undergoes a change in electric potential of 12V, how much energy is involved? ... please explain, I missed class and am having trouble understanding...
 Feb 26th 2009, 09:29 PM #2 Senior Member   Join Date: Dec 2008 Location: Las Cruces NM Posts: 256 "Ah" = Amp hours? Then you can answer 1) by using the definition of a an Amp. 1 Amp is a "rate of flow" of 1 coulomb per second. You can pretend that 84 Amp hours means (84 Amp)(1 hour) To make progress, you must convert Amps to coulombs per second and convert 1 hr to seconds. (84 Amp hours could also mean 42 Amps flow in 2 hours, but you would get the same answer if you decrease the Amps and increase the seconds properly.) You can measure energy in Joules or Watt-hours or kilowatt-hours etc. Let's try Joules. A Watt is the the unit of power equal to 1 joule of energy per 1 second. So 1 watt = (1 joule)/ (1 second) and 1 joule = (1 watt)(1 second) 1 Watt is also equal to (1 volt)(1 amp), though this may not be obvious. So 1 joule = (1 Watt)( 1 second) = (1 volt)(1 amp)/ (1 second) Replace 1 volt by 12 volts, replace 1 amp by 84 amps and replace 1 second by the number of seconds in an hour to get the number of watts.

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