Circuits with Series and Parallel Wiring

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Homework Help Overview

The discussion revolves around a circuit problem involving series and parallel resistors, specifically two 10-ohm resistors, a 20-ohm resistor, and a 6-ohm resistor. Participants express confusion about the configuration of these resistors and how to approach the problem using known equations for series and parallel circuits.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants attempt to identify the arrangement of resistors, questioning whether certain resistors are in series or parallel. There are discussions about redrawing the circuit for clarity and the implications of current flow through different components.

Discussion Status

The discussion is active, with various interpretations of the circuit configuration being explored. Some participants provide insights into the relationships between the resistors and current flow, while others express uncertainty about how to proceed with calculations. There is no explicit consensus on the correct approach yet.

Contextual Notes

Participants mention the need for voltage information to solve for current and discuss the implications of Kirchhoff's laws in relation to the circuit. There are indications of confusion regarding the readings of the ammeter and the calculations of current through the resistors.

Snape1830
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I attached the problem. I'm pretty confused. I remember the equations for parallel and series circuits, but I have no idea how to do this. I attempted, but failed. I know the two 10 ohm resistors are in parallel (so Rnet is 5), and the 20 ohm and the 6 ohm resistor are in series (So Rnet is 26). But then are those in parallel or series? And then i just don't know how to do the problem.
 

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The 10-ohm resistors are in parallel, but the 20-ohm and 6-ohm resistor aren't in series.
 
vela said:
The 10-ohm resistors are in parallel, but the 20-ohm and 6-ohm resistor aren't in series.

Is the 10, 10 and 20 ohm in parallel and the 6 ohm in series with those three? Otherwise, I can't see how the 20 and the 6 aren't in series.
 
The 20-ohm and 6-ohm are not in series because there's something else connected to the node where the two resistors are connected. If two elements are in series, all of the current in one element has to go through the other element. For example, the battery and the 6-ohm resistor are in series. You should be able to see that all of the current that flows through the battery has to also go through the 6-ohm resistor. That's not the case with the 6-ohm and 20-ohm resistor. Some of the current that goes through the 6-ohm resistor will branch off to go through the 10-ohm resistors.
 
vela said:
The 20-ohm and 6-ohm are not in series because there's something else connected to the node where the two resistors are connected. If two elements are in series, all of the current in one element has to go through the other element. For example, the battery and the 6-ohm resistor are in series. You should be able to see that all of the current that flows through the battery has to also go through the 6-ohm resistor. That's not the case with the 6-ohm and 20-ohm resistor. Some of the current that goes through the 6-ohm resistor will branch off to go through the 10-ohm resistors.

Ok...so how do I do the problem?
 
10 ohm resistors aren't in a series and are parallel but the other two are in a series. I find it easy to see if they are parallel or series by redrawing the diagram to one you are comfortable with. At every split in the wire with resistors, just branch it off.
 
mrcheeses said:
10 ohm resistors aren't in a series and are parallel but the other two are in a series. I find it easy to see if they are parallel or series by redrawing the diagram to one you are comfortable with. At every split in the wire with resistors, just branch it off.

So 20 and 6 are in series? That's what I thought. I'm not really sure how to redraw it. Can you can just help me get the answer?
 
Mrcheeses is wrong. The two resistors are not in series.

See http://www.facstaff.bucknell.edu/mastascu/elessonshtml/Resist/Resist2.html
 
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I redraw the circuit making the wires a bit shorter and moving the ammeter closer to the resistors, but the circuit is equivalent with the original one. Note that the ammeter can be replaced by a single piece of wire. Which resistors are connected in parallel?

ehild
 

Attachments

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  • #10
Yes, 10,10 and 20 ohms are in parallel.
 
  • #11
ehild said:
I redraw the circuit making the wires a bit shorter and moving the ammeter closer to the resistors, but the circuit is equivalent with the original one. Note that the ammeter can be replaced by a single piece of wire. Which resistors are connected in parallel?

ehild

10, 10 and the 20 ohm resistor are in parallel. So the Rnet is 4 for those? So then do I just use V=RI to solve for current?
 
  • #12
Yes, the resultant of the parallel resistor is 4 ohm. And the resultant is connected to the 6 ohm resistor, and the whole is connected to the battery. You can use V=RI to get the total current.

What current does the ammeter read?
 
  • #13
ehild said:
Yes, the resultant of the parallel resistor is 4 ohm. And the resultant is connected to the 6 ohm resistor, and the whole is connected to the battery. You can use V=RI to get the total current.

What current does the ammeter read?

Well, 4+6=10.
So...
20=10I
I=2 A

But 2 is wrong, so I don't know.
 
  • #14
The ammeter does not read the current flowing through the battery. It reads the current that flows through itself. It is connected in series with what ?

ehild
 
  • #15
ehild said:
The ammeter does not read the current flowing through the battery. It reads the current that flows through itself. It is connected in series with what ?

ehild

The three resistors in parallel? But to find current you need to know the voltage.
 
  • #16
Snape1830 said:
The three resistors in parallel? But to find current you need to know the voltage.

No it is not the three resistors in parallel, but?
And you can find the voltage. ehild
 
  • #17
ehild said:
No it is not the three resistors in parallel, but?
And you can find the voltage.


ehild

Just the two 10s? How do I find the voltage if I only have the resistors?
 
  • #18
Snape1830 said:
Well, 4+6=10.
So...
20=10I
I=2 A

But 2 is wrong, so I don't know.

Now you got 2 Amps flowing through the equilvalent parallel resistors and through 6 Ohms resistor.

Now what is the voltage across each of the parallel resistors?
From this voltage drop, you calculate the current flow.

What is required here is to find the current flowing through the equivalent parallel resistors of two 10 Ohms resistors.
 
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  • #19
azizlwl said:
Now you got 2 Amps flowing through the equilvalent parallel resistors and through 6 Ohms resistor.

Now what is the voltage across each of the parallel resistors?
From this voltage drop, you calculate the current flow.

V-RI
V=10(2)
V=20 V
V=20(2)
V=40 V

So across the 10 ohm resistors, the voltage drop is 20 V
Across the 20 ohm resistor the voltage drop is 40 V?

That 40 can't be right, though?
 
  • #20
Wrong.
With equivalent parallel resistors, you have only 2 resistors. 6 ohms and 4 ohms.
What is the voltage drop across 4 ohms resistor.
This voltage drop is identical to all the resistors in parallel.
Remember the voltage across all resistore in parallel are equal.
 
  • #21
azizlwl said:
Wrong.
With equivalent parallel resistors, you have only 2 resistors. 6 ohms and 4 ohms.
What is the voltage drop across 4 ohms resistor.
This voltage drop is identical to all the resistors in parallel.
Remember the voltage across all resistore in parallel are equal.

Oh, right, I misread the question.
V=2(4)
V=8 Volts
 
  • #22
Snape1830 said:
Oh, right, I misread the question.
V=2(4)
V=8 Volts

So the voltage across the resultant of the parallel resistors is 8 V. You get the current through each of them if you divide that 8 V by the resistances.
What is the current that flows through the ammeter?
Remember Kirchhoff's nodal law.

ehild
 

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  • #23
ehild said:
So the voltage across the resultant of the parallel resistors is 8 V. You get the current through each of them if you divide that 8 V by the resistances.
What is the current that flows through the ammeter?
Remember Kirchhoff's nodal law.

ehild

Kirchoff's loop rule? The current going in equals the current coming out.
So do I find the current through of the parallel resistors and then add them up...because that comes out to 2 and 2 is wrong.
 
  • #24
Snape1830 said:
Kirchoff's loop rule? The current going in equals the current coming out.
So do I find the current through of the parallel resistors and then add them up...because that comes out to 2 and 2 is wrong.

I wrote Kirchhoff's node rule.

The ammeter measures the current that flows through it. Does I20 ,represented by the green arrow flow through the ammeter?

ehild
 
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  • #25
ehild said:
Wrote Kirchhoff's node rule.

The ammeter measures the current that flows through it. Does I20 ,represented by the green arrow flow through the ammeter?

ehild

No? So it would be 1.6 A?

And thanks for taking the time to edit the picture!
 
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  • #26
Snape1830 said:
No? So it would be 1.6 A?


Correct .

ehild
 
  • #27
ehild said:
Correct .

ehild

Ok! So now part b how much power dissipated through a 10 ohm resistor. The power equation.
P=IV
or
P=I2(r)
or
P= v2/R

I tried a few answers but none of them work.
 
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  • #28
What is the voltage across the 10 ohm resistor?

ehild
 
  • #29
ehild said:
What is the voltage across the 10 ohm resistor?

ehild

8? It seems wrong for some reason
 
  • #30
Snape1830 said:
Ok! So now part b how much power dissipated through a 10 ohm resistor. The power equation.
P=IV
or
P=I2(r)
or
P= v2/R

I tried a few answers but none of them work.
They don't? http://img690.imageshack.us/img690/3484/hidden17.gif

How much current is flowing in just one of the 10Ω resistors?
 
Last edited by a moderator:

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