Circuit Analysis Question: Find Req, i, Vx

In summary, the conversation discusses a simple circuit analysis question with a picture provided for reference. The main objectives are to find the equivalent resistance seen from nodes BC, the current entering the potential source from above, and the voltage across a specific resistor. The results are summarized as Vx = 20 V, Req = 2.079 ohms, and i = 4 A, although there is some uncertainty about the accuracy of these answers. The conversation also briefly mentions the use of Thevenin's equivalent and provides alternative answers for Vx and i.
  • #1
xanadol
9
0
I had a simple circuit analysis question and the picture describes everything; I'll restate the questions just in case if you can't read it.

Find the Req seen from nodes bc, which are the nodes above and below the potential source.
Find the current, i. That is the current enters the potential source from above.
Find Vx, that is the V across the 10 ohm resistor that is parallel with the 4 and 6 in the left bottom mesh.

Let's see who's trading trick or treating with a circuitry problem.

http://img202.imageshack.us/img202/585/dsc02764n.jpg


http://img202.imageshack.us/img202/585/dsc02764n.th.jpg
 
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  • #2
my results were Vx = 20 V
Req = 2.079 ohms
i = 4 A

I'm not sure if they are correct though.
 
  • #3
For what it's worth, my answers are the same, except for the current supplied by the voltage source. Really, this is a simple, simple circuit once you get through realizing which branches are in parallel (and simplifying them, of course).

Note that the voltage source is hooked up between terminals B and C. If you've learned Thevenin's equivalent, you know that you can reduce all the resistances to a black box. If not, note that you found the resistance [itex]R_{BC}[/itex], the resistance seen by anything hooked up between terminals B and C.
 
  • #4
vx can't be 20 because it's not parallel to the potential source. the value of vx i found was 8.71 and i was 9.61 is this what you came up with?
 
  • #5
Oops! I totally misread your response! I got the value of [itex]V_{x}=V_{AC}=11.4 V[/itex] However, I also got the current to be 9.61 A (with some lost numbers as a result of not carrying forward calculations).
 
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1. What is Req in circuit analysis?

Req, or equivalent resistance, is the single resistance value that can replace a set of resistors in a circuit and produce the same current flow and voltage drop as the original set. It is calculated using the formula Req = R1 + R2 + ... + Rn.

2. How do you find Req in a series circuit?

In a series circuit, Req is simply the sum of all the resistances in the circuit. So, if there are three resistors in series with values of 10 ohms, 20 ohms, and 30 ohms, then Req = 10 ohms + 20 ohms + 30 ohms = 60 ohms.

3. How do you find Req in a parallel circuit?

In a parallel circuit, the equivalent resistance is calculated using the formula 1/Req = 1/R1 + 1/R2 + ... + 1/Rn. So, if there are three resistors in parallel with values of 10 ohms, 20 ohms, and 30 ohms, then 1/Req = 1/10 ohms + 1/20 ohms + 1/30 ohms = 0.1667 ohms. Therefore, Req = 1/0.1667 ohms = 6 ohms.

4. How do you find the current (i) in a circuit?

The current (i) in a circuit can be found using Ohm's Law, which states that current is equal to voltage divided by resistance. So, if the voltage in the circuit is 12 volts and the equivalent resistance is 6 ohms, then i = 12 volts / 6 ohms = 2 amps.

5. How do you find the voltage (Vx) in a circuit?

The voltage (Vx) in a circuit can be found by using a voltage divider formula, Vx = (R2 / (R1 + R2)) * Vin, where R1 and R2 are resistors in series and Vin is the input voltage. Alternatively, Vx can be found using Kirchhoff's Voltage Law, which states that the sum of all voltages in a closed loop is equal to zero. This means that Vx can be found by subtracting the voltage drops across each resistor from the input voltage.

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