I am beginning to play around with electronic circuits and have some  basic questions. (Sorry, dont want to dummy-fy the forum!)

Say I have a 12v DC 1amp power supply. I connect a 470ohm resistor to this power supply, and on the opposite side of the resistor I have 12v/25ma, correct? I have 12watts on the supply side, and 0.3 watts on the opposite side of the resistor. Does my resistor need to be rated for 12 watts or 0.3 watts?

Finally, does it affect my resistor either way if my supply is 1 amp or if my supply is 1200 amps? Or if my supply voltage is 5v or 20v? I guess I'm thinking of the current in terms of water pressure, and wondering if the resistor would melt or explode with too much current applied to it. Thanks for any replies! 
Posted on 2005-08-18 00:06:26 by The Dude of Dudes
We were all once a beginner, so I think it is alright to ask dumb questions to get the correct concepts.

Your analogy is wrong. Voltage is supposed to be the water pressure and current the amount of water that flows. Remember the defining equation for current is I = dq/dt which is simplified to I = Q/t for steady current (charge flow).

We always go back to Ohm's law. I = V/R. So even if the power supply can supply at most 1ampere of current, the current through the circuit is only 12/470 A.

A resistor will only melt if its wattage is exceeded (P = I?R).
Posted on 2005-08-18 02:21:48 by roticv
Hello, The Dude of Dudes?

if every electrocircuit want to work normally, you must select appropriate parameter of every component in the electrocircuit. the import parameter is power. the working power of every component must less than or equal than the max power of every component (the parameter is provided by manufacturer). U and I determine the electrocircuit performance. P provide the capacity of the electrocircuit performance.

there are two types DC power supply. One is the DC power supply of the constant electrical current, the resistor in the DC power supply--->0; Another is the DC power supply of the constant electrical voltage, the resistor in the DC power supply--->very huge.

about power supply:
if P>Pmax, then the power supply can't work normally.

about resistor:
if P>Pmax, then the resistor can't work normally(melt or explode).

another question.
are you The Dude of Dudes in www.masmforum.com ?


Posted on 2005-08-18 02:35:52 by dcskm4200
Thanks for the replies! You've both been very helpful! And yes, I occasionally post on the other Forum as well. ;)
Posted on 2005-08-18 22:36:13 by The Dude of Dudes