Need help with a circuit problem? (Picture attached)

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In summary, the current through the 13 Ω resistor is .795 A. The current through the 17.2 Ω resistor is .638 A. The current through the 8.41 Ω resistor is .87 A. The current through the 4.11 Ω resistor is .87 A. The current through the 15 Ω resistor is 2.3 A. The current through the 12.56 Ω resistor is 2.3 A.
  • #1
ObviousManiac
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**PICTURE ATTACHED AT BOTTOM**

Homework Statement


The current in the 13.8-Ω resistor in the attached picture is .795 A. Find the current in the other resistors in the circuit.

Homework Equations


V=RI

In a series circuit:
V of Circuit = V1 + V2 + V3 +...Vn
I of Circuit = I1 = I2 = I3 = ...In
R of Circuit = R1 + R2 + R3 +... Rn

In a parallel circuit:
V of Circuit = V1 = V2 = V3 = ... Vn
I of Circuit = I1 + I2 + I3 +... In
1/R of Circuit = 1/(R1) + 1/(R2) + 1/(R3) +... 1/(Rn)

The Attempt at a Solution



For the 13.8-Ω resistor, I found that Voltage = 10.971 by using V=IR
- Because V of Circuit = (V1 = V2 = V3 = ... Vn), the Voltage for the 17.2-Ω resistor is also 10.971
--Based on this, the Current for the 17.2-Ω resistor is .638:
V=IR
I=V/R
I=(10.971)/(17.2)
I=.638

After this, I proceeded to find the equivalent resistance for the entire circuit.

To find this, I separated the circuits into groups.

Group 1= the 15-Ω and 12.5-Ω resistors (they are in series).
Group 2= the 13.8-Ω and 17.2-Ω resistors (they are parallel).
Group 3= the 8.45-Ω and 4.11-Ω resistors (they are in series).

When solved for, the equivalent resistance for each group is as follows:

Group 1= 27.5-Ω
Group 2= 7.66-Ω
Group 3= 12.56-Ω

Note that Groups 2 and 3 are now parallel. We will combine them into Group 4.

Group 4 Resistance = 4.75-Ω

Now we only have Groups 1 and 4 left in series. When combined, we will get the net resistance for the entire Circuit. This works out to be 32.56-Ω
...So that's everything I could find, which is decent, but doesn't come anywhere near answering the question. I know I must be missing something somewhere.

How do I figure out the individual currents for each resistor with the information I currently have?
 

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  • #2
ObviousManiac said:
**PICTURE ATTACHED AT BOTTOM**

Homework Statement


The current in the 13.8-Ω resistor in the attached picture is .795 A. Find the current in the other resistors in the circuit.

Homework Equations


V=RI

In a series circuit:
V of Circuit = V1 + V2 + V3 +...Vn
I of Circuit = I1 = I2 = I3 = ...In
R of Circuit = R1 + R2 + R3 +... Rn

In a parallel circuit:
V of Circuit = V1 = V2 = V3 = ... Vn
I of Circuit = I1 + I2 + I3 +... In
1/R of Circuit = 1/(R1) + 1/(R2) + 1/(R3) +... 1/(Rn)

The Attempt at a Solution



For the 13.8-Ω resistor, I found that Voltage = 10.971 by using V=IR
- Because V of Circuit = (V1 = V2 = V3 = ... Vn), the Voltage for the 17.2-Ω resistor is also 10.971
--Based on this, the Current for the 17.2-Ω resistor is .638:
V=IR
I=V/R
I=(10.971)/(17.2)
I=.638

After this, I proceeded to find the equivalent resistance for the entire circuit.

<snip!>

You're doing so well using the voltage across the 13.8Ω resistor, why not continue? The same voltage must be across the series connected 8.45Ω + 4.11Ω resistors. So what's the current through them?

What then is the total current for the subcircuit?

attachment.php?attachmentid=41965&stc=1&d=1323922442.gif
 

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  • #3
Ah, of course!

Okay, so based on that...

Current of the 8.45 Ω resistor should be (10.971)/(8.45) = 1.3 A

and the 4.11 Ω will be (10.971)/(4.11) = 2.67 A

So the total for the subcircuit will be

.795 A
+.638 A
+1.3 A
+2.67 A

= 5.403 A

...
Would that be correct?
 
  • #4
ObviousManiac said:
Ah, of course!

Okay, so based on that...

Current of the 8.45 Ω resistor should be (10.971)/(8.45) = 1.3 A

and the 4.11 Ω will be (10.971)/(4.11) = 2.67 A

So the total for the subcircuit will be

.795 A
+.638 A
+1.3 A
+2.67 A

= 5.403 A

...
Would that be correct?

No, not quite. The 8.45 and 4.11 resistors are in series. How do you combine series resistances?
 
  • #5
gneill said:
No, not quite. The 8.45 and 4.11 resistors are in series. How do you combine series resistances?

So would it be

(10.971)/(8.45+4.11) = .873 A

And then the subcircuit would work out as

.873 A
+ .795 A
+ .638 A

= 2.3 A
 
  • #6
ObviousManiac said:
So would it be

(10.971)/(8.45+4.11) = .873 A

And then the subcircuit would work out as

.873 A
+ .795 A
+ .638 A

= 2.3 A

Yessir. That looks good. You should now be in a position to state the current through every resistor in the circuit.
 
  • #7
Alrighty, here are my final results. Everything seems to check out:

13 Ω = .795 A
17.2 Ω = .638 A
8.41 Ω = .87 A
4.11 Ω = .87 A
15 Ω = 2.3 A
12.56 Ω = 2.3 A
 
  • #8
ObviousManiac said:
Alrighty, here are my final results. Everything seems to check out:

13 Ω = .795 A
17.2 Ω = .638 A
8.41 Ω = .87 A
4.11 Ω = .87 A
15 Ω = 2.3 A
12.56 Ω = 2.3 A

Yup.
 
  • #9
thanks for all the help.
 

1. How do I read the circuit diagram in the picture?

To read the circuit diagram, start at the left and follow the path of the wires. The components, such as resistors and capacitors, are represented by different symbols. The lines connecting the components represent wires, and any branches in the circuit indicate parallel connections.

2. What is the purpose of the circuit in the picture?

Without more context, it is difficult to determine the specific purpose of the circuit. However, based on the components shown, it appears to be a simple series circuit used to control the flow of electricity.

3. How do I calculate the total resistance of this circuit?

To calculate the total resistance, you will need to use Ohm's Law, which states that resistance (R) is equal to voltage (V) divided by current (I). You will also need to use the rules for calculating resistance in series and parallel circuits. It is recommended to consult a textbook or online resources for a step-by-step guide.

4. Can you help me troubleshoot a problem with this circuit?

Unfortunately, without more information about the specific issue you are having, it is difficult to provide troubleshooting advice. It is recommended to check all connections and components, and use a multimeter to test for continuity and voltage at different points in the circuit.

5. How can I improve this circuit or make modifications to it?

To improve or modify the circuit, you will need to have a clear understanding of its purpose and how the components work together. From there, you can experiment with different values for resistors or capacitors, or add or remove components to achieve a desired outcome. It is recommended to research and consult with others before making any modifications to a circuit.

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