- #1
zetologos
- 1
- 0
Homework Statement
I don't know where to start. Can anyone recommend a book the instructor didn't assign one.
Equivalent resistance between points a and b
- Thread starter zetologos
- Start date
Click For Summary
Homework Help Overview
The discussion revolves around calculating the equivalent resistance between two points in a circuit, specifically points A and B. Participants are exploring concepts related to series and parallel resistances within the context of circuit analysis.
Discussion Character
- Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation
Approaches and Questions Raised
- Participants discuss the necessity of resources for understanding equivalent resistance and suggest focusing on current flow through resistors. There are inquiries about the implications of removing certain resistors and how that affects the equivalent resistance. Some participants propose using test currents to analyze voltage drops and current distribution.
Discussion Status
The discussion is active, with various approaches being suggested. Some participants offer hints and methods for analyzing the circuit, while others express confusion about the setup and the number of resistors involved. There is no explicit consensus, but several lines of reasoning are being explored.
Contextual Notes
Participants are working under the constraints of homework guidelines, which may limit the resources they can use. There is also a mention of symmetry in the circuit that could simplify the analysis.
I don't know where to start. Can anyone recommend a book the instructor didn't assign one.
- #2
ideasrule
Homework Helper
- 2,286
- 0
I don't think a book is necessary, as long as you know how to find the equivalent resistances for parallel and series circuits. For the first question, imagine a current I entering at A and leaving through B. How much current will flow through each of the resistors? You can use this to figure out the voltage drop between the two points.
For the second question, suppose I take off the 3 resistors at the very right. What would the equivalent resistance be between the top-right point and the bottom-right point? You can use this to set up an equation to solve for the equivalent resistance.
For the second question, suppose I take off the 3 resistors at the very right. What would the equivalent resistance be between the top-right point and the bottom-right point? You can use this to set up an equation to solve for the equivalent resistance.
- #3
MATLABdude
Science Advisor
- 1,664
- 6
Welcome to PhysicsForums!
These are more math / problem solving-type questions, rather than straightforward circuit analysis.
Here's a hint for a: consider what happens when you inject a test current 'I_o' into point A, and figure out how the current flows. Then figure out the voltage at each point (V=IR)
For b, consider that you're adding three series resistors in parallel with a single one. And then you're adding another three series resistors in parallel with the one resistor that you just added previously. Consider: you're far down the line, does adding another three resistors change the equivalent resistance by very much? You should end up solving a quadratic equation using this approach.
Good luck!
EDIT: Obviously, adding three resistors at that point changes the resistance at that point. It shouldn't change the resistance very much at the beginning of your resistor chain.
These are more math / problem solving-type questions, rather than straightforward circuit analysis.
Here's a hint for a: consider what happens when you inject a test current 'I_o' into point A, and figure out how the current flows. Then figure out the voltage at each point (V=IR)
For b, consider that you're adding three series resistors in parallel with a single one. And then you're adding another three series resistors in parallel with the one resistor that you just added previously. Consider: you're far down the line, does adding another three resistors change the equivalent resistance by very much? You should end up solving a quadratic equation using this approach.
Good luck!
EDIT: Obviously, adding three resistors at that point changes the resistance at that point. It shouldn't change the resistance very much at the beginning of your resistor chain.
- #4
pgardn
- 656
- 2
The second diagram looks too easy if Points A and B on the circuit are the far right top and bottom "corners" on the circuit. There is only one resistor between points A and B? What am I missing?
- #5
gneill
Mentor
- 20,989
- 2,934
pgardn said:
All the other paths from A to B that pass through all the other resistors
- #6
vk6kro
Science Advisor
- 4,079
- 41
The first one is done by joining together (with wires) points on the cube that must have the same voltage on them, by symmetry.
If they have the same voltage, no current will flow in the new wires, but they make the problem a lot easier. You get a few sets of parallel resistors in series.
If they have the same voltage, no current will flow in the new wires, but they make the problem a lot easier. You get a few sets of parallel resistors in series.
Similar threads
- · Replies 31 ·
- · Replies 11 ·
- · Replies 3 ·
- · Replies 4 ·
- · Replies 4 ·
- · Replies 5 ·
- · Replies 4 ·