Circuit analysis - Potential differences of resistors

In summary, the conversation discussed finding the voltage and current of each resistor in a circuit with known resistance values and voltage. The Kirchoff's Voltage and Current Laws were used to solve for the voltage and current. The final answers are V_1 = 1.83 V, V_2 = 3.77 V, V_3 = 6.2 V, V_4 = 11.8 V, and V_5 = 31.2 V.
  • #1
Baou
6
0

Homework Statement


circuit_4_pic.jpg
[tex]R_1 = 70 \Omega[/tex], [tex]R_2 = 144 \Omega[/tex], [tex]R_3 = 237 \Omega[/tex], [tex]R_4 = 117 \Omega[/tex], [tex]R_5 = 246 \Omega[/tex]; [tex]V_{ab}=43 V[/tex]
I am looking for the voltage of each resistor as well as the current passing through each one.


Homework Equations


Kirchoff's Voltage/Current Laws: The sum of any potential differences across a closed path is zero; current (charge) is conserved, so any current exiting a node is equal to the sum of the currents entering it.
[tex]V = IR[/tex]
[tex]I = \frac VR[/tex]


The Attempt at a Solution


I know [tex]R_{eq}=339\Omega[/tex]. Thus, [tex]I = \frac VR = \frac{43}{339} = .127 A[/tex].

[tex]V_5 = I*R_5=.127*246=31.2 V[/tex]

[tex]V_1+V_2+V_3-V_4=0[/tex]. This is Kirchoff's voltage equation.

[tex]I_1=I_2=I_3[/tex] b/c current is conserved, so [tex]\frac{V_1}{70}=\frac{V_2}{144}=\frac{V_3}{237}[/tex]. I solve for [tex]V_1[/tex] and [tex]V_2[/tex] in terms of [tex]V_3[/tex]: [tex]V_1=\frac{70V_3}{237}[/tex] and [tex]V_2=\frac{144V_3}{237}[/tex].

I know the current through [tex]V_3[/tex] and [tex]V_4[/tex] should sum to .127, so: [tex]\frac{V_3}{237}+\frac{V_4}{117}=.127[/tex].
[tex]V_4=117\left(.127-\frac{V_3}{237}\right)[/tex].

[tex]V_4=V_1+V_2+V_3[/tex] from above, so plugging in everything I get:
[tex]117\left(.127-\frac{V_3}{237}\right)=\frac{70V_3}{237}+\frac{144V_3}{237}+V_3[/tex].

I solve for [tex]V_3[/tex] and then plug that into everything else.
My final answers are: [tex]V_1 = 1.83[/tex], [tex]V_2=3.77[/tex], [tex]V_3=6.2[/tex], [tex]V_4=12.8[/tex], [tex]V_5=31.2[/tex]. However, these answers are incorrect, so I was hoping to find out what I'm doing wrong.
 
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  • #2
Hi Baou, welcome to PF.
Voltage across R4 = V4 = 43 - V5 = 43 - 31.2 = 11.8 V
 
  • #3
Could you explain how you arrived at that? I don't quite follow...

Edit: Oh, you mean it should be 11.8 instead of 12.8? Was everything else that I did correct?

Edit2: Okay, I was just reading the answer on the calculator wrong. Thanks for the help!
 
Last edited:

1. What is circuit analysis?

Circuit analysis is the process of studying and understanding the behavior of electrical circuits. It involves determining the voltage, current, and power at different points in a circuit to determine how the circuit will function.

2. What is a potential difference?

Potential difference, also known as voltage, is the difference in electrical potential between two points in a circuit. It is measured in volts and represents the amount of energy required to move a unit of charge from one point to another.

3. How do resistors affect potential difference in a circuit?

Resistors are passive components that resist the flow of current in a circuit. As current flows through a resistor, there is a drop in potential difference across it, which is determined by Ohm's law (V=IR). The greater the resistance, the larger the drop in potential difference.

4. How do you calculate potential difference in a series circuit?

In a series circuit, the total potential difference is divided among the resistors. To calculate the potential difference across a specific resistor, you can use Ohm's law (V=IR) or simply add up the potential differences across each resistor in the circuit.

5. How do you calculate potential difference in a parallel circuit?

In a parallel circuit, the potential difference is the same across each branch of the circuit. This means that the potential difference across each resistor is equal to the total potential difference of the circuit. You can also use Ohm's law (V=IR) to calculate the potential difference across each resistor in a parallel circuit.

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