# quick answer check

Discussion in 'Homework Help' started by ihaveaquestion, May 3, 2009.

May 1, 2009
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Feb 4, 2008
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Yes it is.

3. ### ihaveaquestion Thread Starter Active Member

May 1, 2009
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I've thought that if a current has a choice between two resistances, it will ALWAYS flow to the least of the two resistances... i.e. if I had a 5 ohm resistor and a short circuit wire, no current will flow to the 5 ohm resistor and all the current will flow through the other wire...

1) its curious to me why current is flowing into the 4 ohm resistor at all and not just all through the 2 ohm...

2) what's the equation for current through the 2 ohm resistor, i = (I*R2)/(R1+R2)?

4. ### mik3 Senior Member

Feb 4, 2008
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Current would flow through the 5 ohm resistor too because a short wire has a small resistance, it is not a perfect conductor (0 resistance). Your though that current flows through the least resistance is false. Current flows from all components of a circuit with a value depending on each components characteristics.

You are right about the current through the 2 ohm resistor.

5. ### ihaveaquestion Thread Starter Active Member

May 1, 2009
314
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Thank you for your input mik3...

I'm confused now though...

In the circuit I have linked, we have gone over this in class.. and i turned out to be 1 microamp... the same as the current source.. which suggests what I have been thinking about current flowing to least resistance etc

http://img26.imageshack.us/img26/1148/222kiz.jpg

6. ### mik3 Senior Member

Feb 4, 2008
4,846
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In this example they assume that the resistance of the short wire is 0, that is why.

7. ### ihaveaquestion Thread Starter Active Member

May 1, 2009
314
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Oh, you must have meant in real life or something... all of the problems that I am concerned with for the time being are 'ideal' so the resistance of the short circuit wires is 0..

So I suppose the case is that if I have two paths that BOTH have resistances, the current will be split up with more of it going to the lesser of the two resistances, but still some current going to the other path nonethless...

If one path is a short and the other a resistance though, ALL of the current will flow to the short I guess...

8. ### mik3 Senior Member

Feb 4, 2008
4,846
63

A real short does not work like that. A real short has a small resistance and thus a small amount of current will flow through the resistor too.

9. ### Ratch New Member

Mar 20, 2007
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ihaveaquestion,

Yes, your terminology is incorrect. Current does not flow. Current exists. Charge flows. Current is charge flow. To say "current flow" is to say "charge flow flow". The world does not seem to realize that or does not care. Current has a value, but it does not flow twice.

The charge flow is determined by the easily derived and widely used current division principle. The current in R1 of a two resistor parallel circuit is It*R2/(R1+R2) . If R2 is open, the current in R1 is It. If R2 is shorted, then the current in R1 is zero.

Ratch

10. ### paulaubert New Member

May 6, 2009
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change the battery voltage to 9v what is the new voltage across light bulb #2