I am having some difficulties solving a combination circuits problem

In summary, I was trying to find the voltage across a 9-ohm resistor, not the 20-ohm resistor. I got the voltage by adding the currents of the two resistors (8-ohm and 16-ohm) together that were in parallel and it becomes the current that will flow through the 20-ohm resistor. After getting 15V, I don't know what to do next in order to find the current in the 9 - ohm resistor. The voltages across the 8-ohm and 16-ohm resistors are the same, but the voltage across the 20-ohm resistor is different.
  • #1
EddyBenzen122
11
2
Homework Statement
The current in the 8 - ohm resistor in the drawing is 5 A. Find the current in the 20 ohm and 9 - ohm resistor.
Relevant Equations
V = IR
I'm having difficulties finding the current for a 9-ohm resistor only, not the 20-ohm

My attempt was to find the voltage of a 20ohm resistor which is V = (0.75A)(20-ohm) = 15V. I got the 0.75A by adding the currents of the two resistors (8-ohm and 16-ohm) together that were in parallel and it becomes the current that will flow through the 20-ohm resistor. After getting 15V, I don't know what to do next in order to find the current in the 9 - ohm resistor.
Also, look at the image for more information.
 

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  • #2
EddyBenzen122 said:
Homework Statement:: The current in the 8 - ohm resistor in the drawing is 5 A. Find the current in the 20 ohm and 9 - ohm resistor.
Relevant Equations:: V = IR

I'm having difficulties finding the current for a 9-ohm resistor only, not the 20-ohm

My attempt was to find the voltage of a 20ohm resistor which is V = (0.75A)(20-ohm) = 15V. I got the 0.75A by adding the currents of the two resistors (8-ohm and 16-ohm) together that were in parallel and it becomes the current that will flow through the 20-ohm resistor. After getting 15V, I don't know what to do next in order to find the current in the 9 - ohm resistor.
Also, look at the image for more information.
What other voltages can you determine?
 
  • #3
haruspex said:
What other voltages can you determine?
4Volts from the parallel circuits with an 8-ohm and 16 - ohm
 
  • #4
EddyBenzen122 said:
4Volts from the parallel circuits with an 8-ohm and 16 - ohm
So what is the voltage across the ##9 \Omega ##|| ##18 \Omega## pair?
 
  • #5
haruspex said:
So what is the voltage across the ##9 \Omega ##|| ##18 \Omega## pair?
that's what I'm looking for in order to find its current next.
 
  • #6
EddyBenzen122 said:
that's what I'm looking for in order to find its current next.
What is the relationship between the voltages:
- across the 9Ω|| 18Ω pair
- across the 8Ω|| 16Ω pair
- across the 20Ω resistor
?
 
  • #7
haruspex said:
What is the relationship between the voltages:
- across the 9Ω|| 18Ω pair
the voltages are the same for both resistors
haruspex said:
- across the 8Ω|| 16Ω pair
the voltages are the same for both resistors
haruspex said:
- across the 20Ω resistor
haruspex said:
?
the voltage is the sum of the currents for the 8-ohm resistor and the 10-ohm resistor multiplied by the 20-ohm resistor.
 
  • #8
EddyBenzen122 said:
the voltages are the same for both resistors
I didn't ask how the voltage across one of a pair compared with the voltage across the other of the pair. I asked about the relationship between the voltage across the 9Ω|| 18Ω pair (taken as a pair), the voltage across the 8Ω|| 16Ω pair (taken as a pair) and the voltage across the 20Ω resistor. Three voltages, one relationship.
EddyBenzen122 said:
the voltage is the sum of the currents for the 8-ohm resistor and the 10-ohm resistor multiplied by the 20-ohm resistor.
I have no idea how you arrive at that.
 
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  • #9
I have no idea why you're asking me about the relationships between them, are you just giving me a hint?
 
  • #10
EddyBenzen122 said:
I have no idea why you're asking me about the relationships between them, are you just giving me a hint?
Of course I am giving a hint!

Call the voltage at the right of the 20 Ohm resistor 0.
So what is the voltage at the right of the 9||18 pair?

What is the voltage at the left of the 20 Ohm?
So what is the voltage at the left of the 8||16 pair?
So what is the voltage at the left of the 9||18 pair?
 
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  • #11
haruspex said:
Of course I am giving a hint!

Call the voltage at the right of the 20 Ohm resistor 0.
So what is the voltage at the right of the 9||18 pair?
What is the voltage at the left of the 20 Ohm?
So what is the voltage at the left of the 8||16 pair?
So what is the voltage at the left of the 9||18 pair?
K, i got the voltages: 4volts for 8||16 pair, 15V for 20ohm, and 19V for 9||18 pair.
Are they correct?
 
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  • #12
EddyBenzen122 said:
K, i got the voltages: 4volts for 8||16 pair, 15V for 20ohm, and 19V for 9||18 pair.
Are they correct?
Yes.
 
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  • #13
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  • #14
haruspex said:
Yes.
Thanks for helping me, I really appreciate it!
 
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Related to I am having some difficulties solving a combination circuits problem

What is a combination circuit?

A combination circuit is an electrical circuit that contains both series and parallel components. This means that some components are connected in a series, while others are connected in parallel.

What are the common difficulties in solving combination circuits problems?

Some common difficulties in solving combination circuits problems include determining the correct equivalent resistance, applying the correct circuit laws and the use of complex equations, and identifying the direction of current flow in the circuit.

How can I approach solving a combination circuits problem?

To solve a combination circuits problem, it is important to first identify the different components in the circuit and their connections. Then, you can use circuit laws such as Ohm's law and Kirchhoff's laws to analyze the circuit and determine the equivalent resistance. Finally, you can use this information to calculate the current and voltage at different points in the circuit.

What are some tips for solving combination circuits problems?

Some tips for solving combination circuits problems include breaking the circuit down into smaller parts, using a systematic approach, and double-checking your calculations. It can also be helpful to draw a diagram or use a simulator to visualize the circuit.

What are some resources for learning more about combination circuits?

There are many online resources available for learning more about combination circuits, including tutorials, videos, and interactive simulations. You can also consult textbooks or seek help from a teacher or tutor. Practice problems and exercises can also be helpful in improving your understanding and skills in solving combination circuits problems.

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