Voltage in a Circuit: Find Vx with 2A and 6Ω

In summary, the conversation discusses determining the voltage, Vx, in a circuit where 2A passes through a 6Ω resistor. Using the equation V=IR, the voltage is found to be 12V. The total resistance is then calculated to be 9Ω. By finding the current through the parallel combination of the 6Ω and 12Ω resistors, the total current in the circuit is determined to be 3A. Finally, using Kirchoff's laws, the voltage is found to be 27V.
  • #1
Schaus
118
5

Homework Statement


Determine the voltage, Vx, if 2A passes through the 6 Ω resistor.

L1NtWLCm1a0wxW9eO_vHJx7pl1WFfqL8ZIyb85_u8nhNaeAK4JhKeXwbDTNeADXP5hRGEYuuGXqsFu3Hyqf=w382-h170-no.png


Homework Equations


V = IR

The Attempt at a Solution


1/Req=2/12Ω + 1/12Ω = 3/12Ω
Reciprocal of 3/12Ω = 12/3 = 4 Ω

I=2A
R=6 Ω
V = IR
V = (2A)(6 Ω)
V = 12V

Total resistance is 4 Ω + 3 Ω + 2 Ω = 9 Ω
The answer is supposed to be 27V but I don't know how to get it.
 
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  • #2
So far so good!
You know the voltage across the 6Ω and 12Ω resistors. You therefore know or can calculate the current through each and the total current from the source.

If you know the current from the source, then you know the current through the other two resistors and can calculate the voltage across them.

Then you know all the voltages and can work out the source voltage.
 
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  • #3
Schaus said:

Homework Statement


Determine the voltage, Vx, if 2A passes through the 6 Ω resistor.

L1NtWLCm1a0wxW9eO_vHJx7pl1WFfqL8ZIyb85_u8nhNaeAK4JhKeXwbDTNeADXP5hRGEYuuGXqsFu3Hyqf=w382-h170-no.png


Homework Equations


V = IR

The Attempt at a Solution


1/Req=2/12Ω + 1/12Ω = 3/12Ω
Reciprocal of 3/12Ω = 12/3 = 4 Ω

I=2A
R=6 Ω
V = IR
V = (2A)(6 Ω)
V = 12V

Total resistance is 4 Ω + 3 Ω + 2 Ω = 9 Ω
The answer is supposed to be 27V but I don't know how to get it.
Welcome to the PF.

I would approach this problem a little differently. Since we are given 2A through the 6 Ohm resistor, that gives you the 12V number that you got in your work. But that then gives you the current through the 12 Ohm resistor too, right? So what is the total current flowing around the loop?

Then use the parallel combination of the 6 Ohm and 12 Ohm resistors plus the other series resistors and that current to tell you the source voltage. Makes sense?
 
  • #4
I agree with Berkeman. I was just trying to follow through with your approach.
 
  • #5
Merlin3189 said:
I agree with Berkeman. I was just trying to follow through with your approach.
Either way should work. I just like to look for the easiest way to approach a circuit problem, where possible. Many times there is no simple way... :smile:
 
  • #6
So you're saying I take the 12V from the 6 Ohm and 12 Ohm. Then take (2A)(3Ohm) + (2A)(2Ohm)? Because that would be 12V + 6V + 4V = 22V and the answer I am given is 27V
 
  • #7
Schaus said:
So you're saying I take the 12V from the 6 Ohm and 12 Ohm. Then take (2A)(3Ohm) + (2A)(2Ohm)? Because that would be 12V + 6V + 4V = 22V and the answer I am given is 27V
I'm not following what you are saying. The 2A through the 6 Ohms means there is 12V across both the 6 Ohm and 12 Ohm resistors. What does that make the total current through the parallel combination of those two resistors?
 
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  • #8
berkeman said:
I'm not following what you are saying. The 2A through the 6 Ohms means there is 12V across both the 6 Ohm and 12 Ohm resistors. What does that make the total current through the parallel combination of those two resistors?
Ok if I have this straight then I can use I=V/R I = 12V/18Ohms = 0.6667 A? If so I am still unsure of how I determine the rest of the voltage.
 
  • #9
Schaus said:
12V/18Ohms
Where did that come from? The 12 Ohm and 6 Ohm resistors are in parallel.

What is the current through a 12 Ohm resistor that has 12V across it? :wink:
 
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  • #10
12V/12Ohm = 1A. This gives me 3A. Does this mean I have 3A throughout the whole circuit? Then I can take V = IR V = (3A)(9Ohm) V = 27V
 
  • #11
How about putting your results into the diagram?
You found a voltage. You found an equivalent resistance for the 6 and 12
Then you found an equivalent resistance for the whole circuit.
You can transfer voltages and currents using Kirchoff's ideas.
cct_dec.png
 
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  • #12
Ya I should've done that! Makes perfect sense now! Thanks a lot for the help!
 
  • #13
Schaus said:
Does this mean I have 3A throughout the whole circuit?
Schaus said:
3A)(9Ohm) V = 27V
Yes. :smile:
 
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Related to Voltage in a Circuit: Find Vx with 2A and 6Ω

1. What is voltage in a circuit?

Voltage is a measure of the electrical potential difference between two points in a circuit. It is often referred to as the "pressure" or "force" that drives the flow of electric current through a circuit.

2. How is voltage calculated?

Voltage is calculated by dividing the amount of electrical energy (in joules) by the amount of charge (in coulombs) in a circuit. It is represented by the symbol V and measured in volts.

3. What is Vx in a circuit?

Vx is a specific voltage value in a circuit that is calculated using Ohm's Law, which states that V = I*R (voltage equals current multiplied by resistance). Vx is often used to represent the voltage at a specific point in the circuit, typically between two components.

4. How do you find Vx in a circuit with 2A and 6Ω?

To find Vx in a circuit with 2A and 6Ω, you would use the formula V = I*R. In this case, Vx = 2A * 6Ω = 12V. This means that the voltage at that specific point in the circuit is 12 volts.

5. Why is knowing Vx important in a circuit?

Knowing Vx in a circuit is important because it allows us to understand the flow of electric current and the behavior of components in the circuit. It can also help us troubleshoot and identify any issues that may arise. Additionally, Vx can be used to calculate other important values in a circuit, such as power and resistance.

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