# Repost of a resistance questionWatch

#1
I did post this question weeks ago, but am still unable to do it. It's because of the fact that we didn't study anything about Kirchkoffs rule maybe.
I m trying to locate the position of the current flow, but unable to decide the orange ones.

The question asks to calculate the total resistance from A to B

Some people told me to develop two equation and then solve them simultaneously, but i can't figure out how :/

0
4 years ago
#2
This arrangement is equivalent to 3 resistors in parallel. This gives you the total as R/3
I posted a diagram in the original thread showing how you need to look at the diagram and redrawing it to show this.

By the way.
The current through the middle resistor is in the opposite direction to how you have drawn it.

Here are the currents if you want to know how they split and combine.

#3
(Original post by Stonebridge)
This arrangement is equivalent to 3 resistors in parallel. This gives you the total as R/3
I posted a diagram in the original thread showing how you need to look at the diagram and redrawing it to show this.

By the way.
The current through the middle resistor is in the opposite direction to how you have drawn it.

Here are the currents if you want to know how they split and combine.

This is what i was looking for! Just brilliant. Thank you!

Now I have a few more questions:

1) So as each resistor received a different amount of current, we can say that the connection is parallel right? or is this a rather poor approach?
2) Why the current (I1 - I2 ) did not split after passing through the first resistor?
3) Lastly, why the current in this arrangement did not follow the rule of short circuit that it should pass through the lower resistance path?
0
4 years ago
#4
(Original post by Daniel Atieh)
This is what i was looking for! Just brilliant. Thank you!

Now I have a few more questions:

1) So as each resistor received a different amount of current, we can say that the connection is parallel right? or is this a rather poor approach?
2) Why the current (I1 - I2 ) did not split after passing through the first resistor?
3) Lastly, why the current in this arrangement did not follow the rule of short circuit that it should pass through the lower resistance path?
Think about the potential at each junction.

Which junction is at the same potential as point A? Which junction is at the same potential as point B?

Another way to visualise this is to rotate the middle resistor through 1800 anticlockwise.
0
4 years ago
#5
(Original post by Daniel Atieh)
This is what i was looking for! Just brilliant. Thank you!

Now I have a few more questions:

1) So as each resistor received a different amount of current, we can say that the connection is parallel right? or is this a rather poor approach?
It's parallel because of the way it is connected. The problem is that the circuit is drawn in such a way that it conceals the parallel connection.
This is why I redrew the circuit in the original thread to show that it is actually 3 resistors in parallel.
2) Why the current (I1 - I2 ) did not split after passing through the first resistor?
Because the junction on the right of that 1st resistor has a "short circuit" and the current all goes through that lower loop with no resistance.
3) Lastly, why the current in this arrangement did not follow the rule of short circuit that it should pass through the lower resistance path?
It does. See my answer to 2).
#6
(Original post by Stonebridge)

It does. See my answer to 2).
Everything is almost clear to me now. Last thing, why didn't I1 just go through the path of less resistance in the first place? why it split into I2 and I1-I2?
0
4 years ago
#7
(Original post by Daniel Atieh)
Everything is almost clear to me now. Last thing, why didn't I1 just go through the path of less resistance in the first place? why it split into I2 and I1-I2?
I1 splits at the junction because it has a choice of either going through the 1st resistor (far left) OR going round the top loop where it then has to go through either the middle resistor or the far right resistor. (2 choices)

So current coming in from the left either goes through the 1st resistor or it goes through the middle resistor, or it goes through the right resistor before getting to the end. In all cases it takes a route through only one resistor. This is why they are effectively in parallel. The current coming in from the left has three choices. Each choice takes it through only one of the resistors.
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