Kirchhoff's Rules: Circuit Question

[navm1]

Homework Statement

If R₁ is 3Ω, R₂ is 6Ω and R₃ is 9Ω, what are the three currents in figure 16-4, in which the batteries are 6.0v and 12.0v?

Homework Equations

I₁+I₂+I₃

The Attempt at a Solution

I've got three equations so far

I worked out

+6-3I₁-9I₂=0

and

+12-6+6I₂-9I=0

For the next step I have to find I₁ in terms of I₂ but I'm not sure how I do that

http://puu.sh/7ZXv9.png

 

[SammyS]

Homework Statement

If R₁ is 3Ω, R₂ is 6Ω and R₃ is 9Ω, what are the three currents in figure 16-4, in which the batteries are 6.0v and 12.0v?

Homework Equations

I₁+I₂+I₃

The Attempt at a Solution

I've got three equations so far

I worked out

+6-3I₁-9I₂=0

and

+12-6+6I₂-9I=0

For the next step I have to find I₁ in terms of I₂ but I'm not sure how I do that

http://puu.sh/7ZXv9.png

Your subscripts are inconsistent with you equations and/or the figure.

Also, I₁+I₂+I₃ is not an equation. Perhaps you meant I₁+I₂=I₃

 

[navm1]

Your subscripts are inconsistent with you equations and/or the figure.

Also, I₁+I₂+I₃ is not an equation. Perhaps you meant I₁+I₂=I₃

youre right i meant to put I₁+I₂+I₃=0 and

+12-6+6I2-9I₁=0

 

[SammyS]

youre right i meant to put I₁+I₂+I₃=0 and

+12-6+6I2-9I₁=0

12 - 6 + 6I₂ - 9I₁ = 0 is correct.

For I₁+I₂+I₃=0 to be correct, you should draw I₃ in the opposite direction.

You need to correct the other loop equation.

 

[navm1]

12 - 6 + 6I₂ - 9I₁ = 0 is correct.

For I₁+I₂+I₃=0 to be correct, you should draw I₃ in the opposite direction.

You need to correct the other loop equation.

+6-3I₁-9I₂=0

is wrong?

I think i was getting mixed up over some wording in my workbook. I've got

2-3I₂=I₁ now and i'll substitute in the third equation

 

[NascentOxygen]

+6-3I₁-9I₂=0

is wrong?

It looks wrong. Where did it spring from?

I think i was getting mixed up over some wording in my workbook. I've got

2-3I₂=I₁ now and i'll substitute in the third equation

Where did that spring from? If you'd explain the laws you applied to arrive at these, it would make the process of checking your steps easier, ditto for finding mistakes.

Perhaps you have some currents and/or resistors labelled differently to how you think you have?

 

[navm1]

It looks wrong. Where did it spring from?


Where did that spring from? If you'd explain the laws you applied to arrive at these, it would make the process of checking your steps easier, ditto for finding mistakes.

Perhaps you have some currents and/or resistors labelled differently to how you think you have?

the question was "If R₁ is 3Ω, R₂ is 6Ω and R₃ is 9Ω, what are the three currents in figure 16-4, in which the batteries are 6.0v and 12.0v?"

and here's the solution, might make it more clear to you what I am missing

http://puu.sh/80On3.jpg

http://puu.sh/80Oo1.jpg

 

[dauto]

The problem we're having is that the signs and indices in your currents and/or resistors in the equations don't seem to match what we see in the picture. Your first job is to fix that. Than we can talk about how to solve the equations.