# Find Currents & Vab with Reversed Polarity Battery in Circuit

• jelsliger7
In summary: Kirchoff.In summary, the conversation discusses a problem involving a circuit with a 10.00V battery and multiple resistors. The battery is removed and reinserted with the opposite polarity, and the goal is to find the current in each branch and the potential difference between points a and b. The conversation mentions using mesh (or loop) analysis and applying Kirchoff voltage law to solve the problem.
jelsliger7

## Homework Statement

The 10.00V battery in the figure is removed from the circuit and reinserted with the opposite polarity, so that its positive terminal is now next to point a. The rest of the circuit is shown in the figure. Find a, the current in each branch and b, the potential difference Vab of point a relative to point b

## Homework Equations

V = IR
1/Req=1/R1+1/R2+...+1/Rn
Req = R1 + R2 + R3
the sum of the current at each junction =0
the sum of the potential = 0 (loop rule)

## The Attempt at a Solution

R in series
R' = 2+3 = 5
R''= 1+4 = 5

Now in series
1/Req = 1/R' +1/R'' +1/10
=1/5 + 1/5 + 1/10 = 5/10
thus Req = 2.0ohms

I=V/R
I=15/2 = 7.5A

i think i am just confused as to what to do if there are two different voltage supplies, how do i find Req?

#### Attachments

• circuit.jpg
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The fact that they want you to find two branch currents calls for a much easier method. Just use mesh (or loop) analysis. You will get two equations and two unknowns (the branch currents).

To find Vab, just apply KVL around the loop containing points a and b. Better yet, you don't have to go around the entire circuit. Just start at point a, go to straight to b and work your way clockwise back to point a.

Given the topology of the circuit, I'm afraid that there isn't any easy method of finding Req wrt t0 points ab. Besides, you don't need req to solve this problem. Thinking about it only confuses you.

Last edited:
hey i am still confused, how can i only have 2 unknowns when i have multiple resistors won't they all have different currents flowing through them? and then what exactly is the branch current?

sorry i didn't reply earlier i just had my reading week and i was out of town

well if you do not know mesh currents, then use Kirchoff voltage law to make 3 equation with 3 unknowns

## 1. What is the purpose of finding currents and Vab with a reversed polarity battery in a circuit?

The purpose of this procedure is to determine the direction and magnitude of currents flowing through a circuit when the polarity of a battery is reversed. This can help in troubleshooting circuit problems and understanding the behavior of different components in the circuit.

## 2. How do you find the currents and Vab in a circuit with a reversed polarity battery?

To find the currents and Vab, you will need to use Kirchhoff's laws and Ohm's law. First, you will need to redraw the circuit with the reversed polarity battery. Then, you can use Kirchhoff's voltage law to calculate the voltages around the loop and Kirchhoff's current law to determine the currents at each node. Finally, you can use Ohm's law to calculate the voltage drops and currents through each resistor.

## 3. Can the currents and Vab be calculated using a multimeter?

Yes, a multimeter can be used to measure the voltage and current at different points in the circuit. However, it is important to note that using Kirchhoff's laws and Ohm's law will provide more accurate and comprehensive results.

## 4. What are the common mistakes to avoid when finding currents and Vab with a reversed polarity battery?

One common mistake is forgetting to redraw the circuit with the reversed polarity battery. This can lead to incorrect calculations and results. It is also important to correctly apply Kirchhoff's laws and Ohm's law, ensuring that the direction of current flow is accounted for in the calculations.

## 5. Can this procedure be used for circuits with more than two resistors?

Yes, this procedure can be used for circuits with any number of resistors. The principles of Kirchhoff's laws and Ohm's law can be applied to any circuit to determine the currents and voltages. However, as the complexity of the circuit increases, the calculations may become more challenging and time-consuming.

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