Why isn't electricity flowing through this wire?


by remedemic
Tags: electricity, flowing, wire
remedemic
remedemic is offline
#1
Mar18-13, 08:07 PM
P: 19


In the top circuit, electricity doesn't flow through section 2, but it does in section 1.
In the bottom circuit however, electricity flows through both sections 3 and 4. Why does
simply adding a resistor stop the flow of electricity in 2?

Much appreciated!
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jafferrox
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#2
Mar18-13, 08:14 PM
P: 23
current will flow through the easiest path ( without resistance) or with less resistance and as the wire doesn't have any resistance, all the current will flow through it.
remedemic
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#3
Mar18-13, 08:20 PM
P: 19
Quote Quote by jafferrox View Post
current will flow through the easiest path ( without resistance) or with less resistance and as the wire doesn't have any resistance, all the current will flow through it.
In the top circuit, if I add a resistor to section 1 that has less resistance than section 2, electricity will still flow through both, won't it?

jafferrox
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#4
Mar18-13, 08:25 PM
P: 23

Why isn't electricity flowing through this wire?


yeh it will, but the one with more resistance will have less current flowing through it.
remedemic
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#5
Mar18-13, 08:29 PM
P: 19
Quote Quote by jafferrox View Post
yeh it will, but the one with more resistance will have less current flowing through it.
SO, why isn't there just less current (instead of zero current) in section 2 compared to section 1 since it has more resistance?

Thanks for the help by the way, I greatly appreciate it.
jafferrox
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#6
Mar18-13, 08:34 PM
P: 23
it's just how it is, because current has to flow through both of the sections and that most current will flow through the section with less resistance.
remedemic
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#7
Mar18-13, 08:38 PM
P: 19
Quote Quote by jafferrox View Post
it's just how it is, because current has to flow through both of the sections and that most current will flow through the section with less resistance.
im understanding it now. Thank you very much sir.
jafferrox
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#8
Mar18-13, 08:47 PM
P: 23
glad you understood it, your welcome.
MrAnchovy
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#9
Mar18-13, 09:09 PM
P: 388
Quote Quote by remedemic View Post
SO, why isn't there just less current (instead of zero current) in section 2 compared to section 1 since it has more resistance?
You are right, there is SOME current in section 2. The ratio of the currents is the same as the ratio of the resistances; 10cm of wire might have a resistance of 0.006Ω so if R3 is 100Ω and 0.1A is flowing through the circuit, 0.1A x 0.006 / 100 = 6μA will be flowing through R3.
davenn
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#10
Mar18-13, 09:25 PM
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Quote Quote by MrAnchovy View Post
You are right, there is SOME current in section 2. The ratio of the currents is the same as the ratio of the resistances; 10cm of wire might have a resistance of 0.006Ω so if R3 is 100Ω and 0.1A is flowing through the circuit, 0.1A x 0.006 / 100 = 6μA will be flowing through R3.
yup, but the main point is that the resistor in section 2 is effectively being shortcircuited

Dave
russ_watters
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#11
Mar18-13, 09:58 PM
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The problem here is one of starting assumptions. If the assumption of the problem is that there is no resistance in the wires (a common assumption), then all of the current has to go through the short. But in real life, there is a finite resistance even in a wire, so a certain amount of current will flow through each branch.
mishima
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#12
Mar18-13, 10:46 PM
P: 282
If you measure the voltage at 2 points on a wire without resistance you get the same result. By short circuiting the resistor in section 2 you are making both ends the same voltage.

The current in an element like a resistor obeys the following:

[Voltage (one end) - Voltage (other end) ] / resistance = current

So as you can see if the voltages are the same you get zero current.
carlgrace
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#13
Mar19-13, 12:31 PM
P: 555
Look up "Current Divider" on Wikipedia. It will explain what is going on quantitatively. If you have a mind for math, this may help you understand better.


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