Circuit with Four Resistors and Two Switches

AI Thread Summary
The discussion revolves around calculating the potential difference Vcd in a circuit with four resistors and two switches, where switch S2 is closed and S1 is open. The user initially attempted to find the total resistance and current but was unsure about their method. They later clarified that with S2 closed, nodes c and d become a single node, prompting a request for guidance on finding the current through the second switch. Participants suggested using Kirchhoff's Current Law (KCL) at node c to determine the voltage drop across each resistor and calculate the current. The conversation emphasizes the importance of correctly applying circuit analysis techniques to solve for potential differences and currents in complex circuits.
Jake Russell
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Homework Statement


Four resistors connected to a battery are shown in the figure (at bottom). The switch S2 is closed and switch S2 is left open. What is the magnitude of the potential difference Vcd

Homework Equations


Rp= Σ(1/Ri)-1

Rs = ∑Ri

V = IR

The Attempt at a Solution


Seeing as c and d aren't directly connected since S2 is open, I attempted to find the total resistance using the two resistance equations above and from that find the total current. After that, I divided the total current by two since the total resistance on both sides are the same, and multiplied that by the total of the top resistance. Next I added the current multiplied by the bottom left resistor and subtracted the current multiplied by the bottom right resistor, but I don't think this is correct.
upload_2016-3-2_18-18-20.png
 
Last edited:
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Hi Jake Russell, Welcome to Physics Forums!

The mage that you tried to attach isn't viewable. Can you upload it again?
 
I ended up figuring out this question (I wasn't starting at a and not c), but I have another one. How would I find the current through the second switch when it is closed?
 
With switch S2 closed can you find the potential at node cd? (Since S2 joins c and d together, they become a single node).

Knowing the potentials at a,b, and c, can you write a KCL equation at location c?
 
Work out the voltage drop across each resistor (easy) then calculate the current in each resistor and mark it on the diagram. Apply KCL at either node c or d.

Edit: cross posted with gneill.
 

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