Electronics > Beginners

(1/3) > >>

kevyk:
A basic electronics question here:

If current can be likened to molecules of water passing a fixed point and voltage can be likened to the difference in pressure between two ends of a water hose, is it possible to have a huge current (say 10000 amps) flowing while the difference between the two ends is very small (say 1 volt)? This question is of course assuming the wire/hose can handle the capacity without failure and offers negligible resistance itself.

If so, I don't understand how this can be because the voltage potential (difference between the two ends) is so little, how would it be possible to have such a high water /current flow?

Make sense?

Neilm:

--- Quote from: kevyk on August 19, 2011, 04:28:48 pm ---A basic electronics question here:

If current can be likened to molecules of water passing a fixed point and voltage can be likened to the difference in pressure between two ends of a water hose, is it possible to have a huge current (say 10000 amps) flowing while the difference between the two ends is very small (say 1 volt)? This question is of course assuming the wire/hose can handle the capacity without failure and offers negligible resistance itself.

If so, I don't understand how this can be because the voltage potential (difference between the two ends) is so little, how would it be possible to have such a high water /current flow?

Make sense?

--- End quote ---

The simple answer is yes. I have seen equipment that will output 2kA at 3V. It does this by the application of Ohms law - R=V/I so the output would have to be less than 1.5m ohms. This would be done by a very high tech piece of equipment - VERY thick wires. See http://www.q80united.com/admincp/files/datasheets/PCITS2000-2.pdf The more current you want to pass, the lower you make the resistance for any given voltage.

10kA would be found in power stations, where they use thick bus bars to carry the current. The voltage over these has to be low or they would overheat and waste power.

Yours

Neil

HLA-27b:

--- Quote from: kevyk on August 19, 2011, 04:28:48 pm ---If current can be likened to molecules of water passing a fixed point.....

--- End quote ---
What you defined so far is the electric charge. To define current you need to say

--- Quote ---If current can be likened to molecules of water passing a fixed point for a fixed amount of time...
--- End quote ---

So 100 electrons passing a fixed point is just some charge changing place. OTOH 1000 electrons passing a fixed point in 1 second denotes an amount of flow i.e. current.

This was the boring bit. The fun bit is that it is perfectly possible to have 10000 amps flowing through a conductor. In fact the superconducting magnets of CERN carry 13000A. The ATLAS experiment carries 21000 A.
http://www.ted.com/talks/brian_cox_what_went_wrong_at_the_lhc.html
http://public.web.cern.ch/press/pressreleases/releases2006/PR17.06E.html

kevyk:
Thanks. This is more of an understanding question than a practical one.

So it sounds like it is possible to have huge currents flowing while the voltage is very very low.

But how can this be if the voltage (potential difference) between the two ends is so small, how is it possible even with a 0 ohm resistance (water hose with no resistance) to have a flow rate so large? What would be pushing the water/electrons so 'fast' (high current) if the potential difference is so low (1 volt)?

Mechatrommer:
well i like this kind of imaginative question. i thougt of roof analogy, but i think waterfall is better one. if you look from above (upstream), the river (before waterfall) they move slowly, but the river has large width, but since the water move slowly, you think it only small amount of water? wrong. the amount is the same when you look from below the waterfall, you'll see massive volume of water falling down fast, they are both the same amount (upstream and downstream)... V=IR... so upstream V is very low, but R is low as well. but downstream V is very high, but R is high as well (bottleneck where the water start falling), so in the end, they are the same I.... massive. the massiveness will depend how much volume of water in the system (start from mountain upstream down to the waterfall), ie how much "energy" in the system. you can have hi potential but low energy system (like electrostatic in your body or van de graff) but you also can have lo potential but hi energy system, like welding machine, you can touch without feeling anything but harmfull to lo resistance conductor.