simple question power, resistance, current, etc
in [Physics]
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From: Peter Webb on 19 Feb 2010 00:03 "Androcles" <Headmaster(a)Hogwarts.physics_u> wrote in message news:znofn.59087$YO.37501(a)newsfe24.ams2... > > "none" <none(a)none.com> wrote in message > news:2010021822033416807-none(a)nonecom... >> Is the "power" of a battery a constant? > > No. > > > I assumed it should be, but >> then I was thinking that if V=IR, say you have a battery with voltage 9 >> and circuits with resistance 3 or 4.5. The current should be 3 or 2, >> respectively. Then, the power would be 27, or 18, if power = voltage * >> current, right? > > Wrong. Power = voltage * current * time. No, Energy = voltage * current * time. Power = voltage * current. > >>So does the power of a batter change depending on the resistance of the >>circuit? Seems odd... >> > Power is measured in kilowatt hours or watt hours. That's what > you pay for. No, power is measured in kilowatts or Watts. Energy is measured in kwH or watt hours. That is what you pay for. Really, if you don't know the difference between power and energy, you are spectacularly unqualified to answer questions about Ohms Law, and should refrain from displaying your ignorance of basic physics in public in this manner.
From: Sam Wormley on 19 Feb 2010 00:55 On 2/18/10 10:03 PM, none wrote: > Is the "power" of a battery a constant? I assumed it should be, but then > I was thinking that if V=IR, say you have a battery with voltage 9 and > circuits with resistance 3 or 4.5. The current should be 3 or 2, > respectively. Then, the power would be 27, or 18, if power = voltage * > current, right? So does the power of a batter change depending on the > resistance of the circuit? Seems odd... > http://hyperphysics.phy-astr.gsu.edu/Hbase/electric/elepow.html#c1
From: Helmut Wabnig hwabnig on 19 Feb 2010 03:26 On Fri, 19 Feb 2010 16:03:27 +1100, "Peter Webb" <webbfamily(a)DIESPAMDIEoptusnet.com.au> wrote: > >"Androcles" <Headmaster(a)Hogwarts.physics_u> wrote in message >news:znofn.59087$YO.37501(a)newsfe24.ams2... >> >> "none" <none(a)none.com> wrote in message >> news:2010021822033416807-none(a)nonecom... >>> Is the "power" of a battery a constant? >> >> No. >> >> >> I assumed it should be, but >>> then I was thinking that if V=IR, say you have a battery with voltage 9 >>> and circuits with resistance 3 or 4.5. The current should be 3 or 2, >>> respectively. Then, the power would be 27, or 18, if power = voltage * >>> current, right? >> >> Wrong. Power = voltage * current * time. > > >No, Energy = voltage * current * time. >Power = voltage * current. > > >> >>>So does the power of a batter change depending on the resistance of the >>>circuit? Seems odd... >>> >> Power is measured in kilowatt hours or watt hours. That's what >> you pay for. > > >No, power is measured in kilowatts or Watts. Energy is measured in kwH or >watt hours. That is what you pay for. > >Really, if you don't know the difference between power and energy, you are >spectacularly unqualified to answer questions about Ohms Law, and should >refrain from displaying your ignorance of basic physics in public in this >manner. > http://en.wikipedia.org/wiki/Power http://en.wikipedia.org/wiki/Energy http://en.wikipedia.org/wiki/Work http://en.wikipedia.org/wiki/Electrical_work http://en.wikipedia.org/wiki/Watt Really, if you don't know the difference between power and energy, you are spectacularly unqualified to answer questions about Ohms Law, and should refrain from displaying your ignorance of basic physics in public in this >manner. w.
From: Darwin123 on 19 Feb 2010 12:40 On Feb 18, 11:23 pm, "Androcles" <Headmas...(a)Hogwarts.physics_u> wrote: > "none" <n...(a)none.com> wrote in message > Wrong. Power = voltage * current * time. <LOL> > > >So does the power of a batter change depending on the resistance of the > >circuit? Seems odd... > > Power is measured in kilowatt hours or watt hours. That's what > you pay for. <LOL> <LOL> > What one pays for is energy, not power.
From: PD on 19 Feb 2010 13:43
On Feb 18, 10:23 pm, "Androcles" <Headmas...(a)Hogwarts.physics_u> wrote: > "none" <n...(a)none.com> wrote in message > > news:2010021822033416807-none(a)nonecom... > > > Is the "power" of a battery a constant? > > No. > > I assumed it should be, but > > > then I was thinking that if V=IR, say you have a battery with voltage 9 > > and circuits with resistance 3 or 4.5. The current should be 3 or 2, > > respectively. Then, the power would be 27, or 18, if power = voltage * > > current, right? > > Wrong. Power = voltage * current * time. > > >So does the power of a batter change depending on the resistance of the > >circuit? Seems odd... > > Power is measured in kilowatt hours or watt hours. That's what > you pay for. > > A one watt-hour battery may deliver a milliamp for a 1000 hours at 1 volt > into a 1000 ohm resistor, or it could deliver 1 amp for 1 hour into a 1 ohm > resistor. > A car battery is 12V nominal and delivers 100 amps (1200 watts) into the > starter motor, but it won't do it for long. Hopefully it doesn't need to, > the engine fires up. > It can deliver 3 amps into a headlight for much longer (36 watts) > but it would take 6 amps for two headlamps and only last half > the time. Oh, good heavens. And you were an engineer? You pay for *energy* not for power. Power is the rate at which that energy is consumed. Energy = voltage * current * time. But feel free to make more stuff up, as long as you're in a slurring stupor. PD |