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How can you tell by looking at a circuit diagram that one of the resistors is in parallel with a short circuit and therefore does not count when adding all the resistors together?
circuit question
- Thread starter thedarkhorse
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since the current has a choice to take the resistor route or no resistor route, it will go with the no resistor.. kind of how if 2 different resistors are in parallel, the less resistance one will get more current..
that's my intuition, but i would have been like wtf if i saw that picture
that's my intuition, but i would have been like wtf if i saw that picture
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1/3+1/6=2/6+1/6=3/6=1/2 -> the equivalent resistance for the two resistors on the right is 2 ohm. Total equivalent is 2+4=6 ohm.
Current is 24V/6Ohm=4 A.
Current through 3 Ohm resistor is twice the current through the 6 Ohm, so you have x+2x =4, 3x=4, x=4/3 A and 2x=8/3 A.
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You missed the part where the top resistor is in parallel with a short. Because of this, the top resistor does not contribute to this circuit at all.
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Yes, it is. The resistor on top is in parallel with a piece of wire with no resistance. As such, the equivalent resistance for that part is 0 Ohm and you can ignore it. The total resistance is only 4+2.
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8/3 is the right answer, and I am able to get that answer when I don't include the 2ohm resistor which is what the explanation in my book said to do, but without reading the explanation I wouldn't know how to disregard it. so does anyone know why I was supposed to ignore the 2 ohms just by looking at the diagram
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Because its terminal are shorted - both ends of the resistor are connected to the same part of the circuit with nothing in between them. That's the same as having them touch each other - the path in parallel to this resistor have no resistance at all.
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i feel so dumb, i get what you're saying but again I think that if I saw a diagram like this in another question I wouldn't know that the resistor is shorted, can you try explaining again how to recognize that
I see how the current is 8/3A once I figured out the eq resistance and all that. But my question is, why isn't the voltage across both parallel resistors on the right just equal to the voltage of the battery? If the resistor up top is shorted, there is no voltage drop so wouldn't 24 volts be applied across each the 3 ohm and 6 ohm resistors?
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There is a voltage drop across the resistor at the bottom.
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D
deleted103644
This should improve things a lot:
I would have made an attempt to be helpful if I could view the OP's circuit diagram.
Since I can't, I thought this was a good compromise.
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It sure was, but you cannot deny that my suggestion would lead to the best outcome for your circuit. 😛
As for OP's circuit - do you see this:
D
deleted103644
It sure was, but you cannot deny that my suggestion would lead to the best outcome for your circuit. 😛
As for OP's circuit - do you see this:
No, using the iPhone app. It doesn't do well with SDN attachments.
D
deleted103644
Mucked around in Safari and finally got it. Not bad at all.
1) Short circuit. Alternatively, you could view it as having a zero ohm resistor in parallel:
R = 1 / (1/2 + 1/x) --> 0 as x approaches 0
2) Parallel:
R = 1/(1/3 + 1/6) = 2
3) R = 4
Add the effective resistors in series together: 0 + 2 + 4 = 6 ohms.
24 V / 6 ohms = 4 amps.
1) Short circuit. Alternatively, you could view it as having a zero ohm resistor in parallel:
R = 1 / (1/2 + 1/x) --> 0 as x approaches 0
2) Parallel:
R = 1/(1/3 + 1/6) = 2
3) R = 4
Add the effective resistors in series together: 0 + 2 + 4 = 6 ohms.
24 V / 6 ohms = 4 amps.
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Wow, nice catch. I didn't even know this was possible lol.
D
deleted103644
If you are ever the short, you'll realize it's very possible (and painful).
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It is pretty intuitive as to why we ignore the shorted resistor.
If the current has a much less resistive path through which it can travel, it will have a higher propensity to go that way. This is observed with every resistor in parallel with another one of unequal resistance.
However, in the short, the other leg of the parallel branch is just the idealized wire that possesses zero resistivity, so all of the current will opt to go through it.
If the current has a much less resistive path through which it can travel, it will have a higher propensity to go that way. This is observed with every resistor in parallel with another one of unequal resistance.
However, in the short, the other leg of the parallel branch is just the idealized wire that possesses zero resistivity, so all of the current will opt to go through it.
