Re: [Phys-l] cars and physics

["Quist, Oren" <Oren.Quist@SDSTATE.EDU>]

I was told this, but never verified it.

One reason cars switched from 6-volt to 12-volt (when I started driving, most cars were 6-volt) was that the time constant to charge up the condenser (what we call the capacitor) was too long to effectively fire eight spark plugs at normal rpm speeds.  As V-8's became popular, the 12-volts became necessary.  Of course the time constant would not change as the voltage went up, but double the voltage would lead to double the charge which was then enough to fire the plugs.  

True or false???   -- whatever, it makes for an interesting calculation.

________________________________________
From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Bill Nettles [bnettles@uu.edu]
Sent: Monday, February 21, 2011 11:13 AM
To: Forum for Physics Educators
Subject: Re: [Phys-l] cars and physics

Another interesting problem is cheap (10 gauge) jumper cables versus better (6 or 4 gauge) cables and their effectiveness (considering the voltage across the cable) in jumping a car with a really dead battery.  Conclusion should be "spend the extra bucks to get the thicker cables."  You need to look at the current drawn by the starter, which can be from 75 to 120 amperes. Students are amazed at how low the resistance is/needs to be.

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Bernard Cleyet
Sent: Sunday, February 20, 2011 7:51 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] cars and physics

Until my auto tool kit disappeared, I had two non-insertion DC ammeters.  One +/- ~ 30A and tother 200?
 I compared them to an insertion one (d'Arsonval w/ shunt and found them w/in ~ 1/4 the ticks.  e.g. not bad.  w/ such the students can do the measurements!

bc thinks obvious why the Auto Store had these two.


On 2011, Feb 20, , at 14:03, Anthony Lapinski wrote:

> I'll be teaching electricity in the coming weeks. Wanted to do some basic
> math problems involving the electrical system of an automobile with a 12-V
> battery. Does anyone know the power (or current) of car devices, or a web
> site that would have this information?
>
> radio
> low beams (50 W?)
> high beams (60 W?)
> heater
> air conditioner
> rear window defroster (72 W?)
> cigarette lighter
>
> _______________________________________________
> Forum for Physics Educators
> Phys-l@carnot.physics.buffalo.edu
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