Berkeley CSUA MOTD:Entry 29230
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2025/05/25 [General] UID:1000 Activity:popular
5/25    

2003/8/4-5 [Science/Electric] UID:29230 Activity:moderate
8/3     What's the relationship between WATT, VOLT, and AMP? I have a power
        supply that is 12V and 2.1Amp, but it is unable to drive a bulb
        that is 12V and 55Watts. I know there is not enough ampere in the
        power supply, but how do you derive the relationship?
        \_ power[Watts] = voltage[Volts] * current[Amps].
           also note that if you're dealing with AC, the current and voltage
           are RMS, not peak to peak.
           \_ 12V, battery power, hence DC. What's RMS? Richard Stallman?
              Average power?
              \_ rms:rms and an internet worm will get you into any host!
              \_ Root Mean Square
                 \_ yes, and from a practical standpoint, for sinusoidal ac
                    currents, it's a factor of 1/sqrt(2) different from peak
                    to peak for voltage, and hence a factor of 2 different
                    in power.
           \_ thank you. So 12V*2.1Amp=25Watts, and I'm ~2.5 Amps short of
              driving the 55W bulb, right?
        \_ Watts is a measurement of power.  You can measure your car's
           horsepower in Watts.
           You can think Amp as measurement of flow rate, similiar to
           how fast water flows out of the toliet water tank when you flush.
           Voltage is pressure.  In order to have water flow from one
           place to another, it need to have differences in pressure.
        \_ What the "VA" used in the battery backup specifications mean?

           Tricky part is to get a feel of what are these units.  For
           example, one Amp is HUGE amount of electricity flow, even with
           reasonably small voltage, it may kill you.
           \_ "it's volts that jolts and mils that kills"
2025/05/25 [General] UID:1000 Activity:popular
5/25    

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