Mesh Analysis Help: Solve Circuit for i1 & i2

[James889]

Hi,

I have the following circuit:
[PLAIN]http://img265.imageshack.us/img265/6476/upg2.png

But when i try to calculate the mesh currents i end up with the wrong answer.

This is what i did:
Equation for i1:
$$6i_1 + 18(i_1-i_2) -30$$
Equation for i2:
$$17i_2 + 18(i_2-i_1) -19$$

Adding currents in the first equation:
$$24i_1 - 18i_2 -30$$

Adding currents in the second equation:
$$35i_2 - 18i_1 -19$$

$$18i_1 = 35i_2 -19$$
$$i_1 = 1.94i_2-1.056$$

Inserting into the first equation i get
$$24(1.94i_2-1.056) - 18i_2 -30$$

Which gives that $$i_2 = 1.93$$ but that's wrong

Where did i go wrong ?

/james

 

[ejk5401]

Hi,

I have the following circuit:
[PLAIN]http://img265.imageshack.us/img265/6476/upg2.png

But when i try to calculate the mesh currents i end up with the wrong answer.

This is what i did:
Equation for i1:
$$6i_1 + 18(i_1-i_2) -30$$
Equation for i2:
$$17i_2 + 18(i_2-i_1) -19$$

Adding currents in the first equation:
$$24i_1 - 18i_2 -30$$

Adding currents in the second equation:
$$35i_2 - 18i_1 -19$$

$$18i_1 = 35i_2 -19$$
$$i_1 = 1.94i_2-1.056$$

Inserting into the first equation i get
$$24(1.94i_2-1.056) - 18i_2 -30$$

Which gives that $$i_2 = 1.93$$ but that's wrong

Where did i go wrong ?

/james

you need to get a determinant for the matrix first notice its a 2 x 2 so you would put it in like this rt in first minus the r they share and the same for the second, then you'd use the voltage on the side [24 -18]30
[-18 35] 19
------------ then you do your matrix and get your first determinate
then you sub in the 30 and the 19 for a then b once you have that its a/d and b/d

 

[The Electrician]

Why do you think your answer is wrong? Is it because the answer given by the textbook (or your instructor) is different? Sometimes textbooks have the wrong answer for problems.

The answer I get is:

I1 = 2.69767
I2 = 1.93023

 

[James889]

Why do you think your answer is wrong? Is it because the answer given by the textbook (or your instructor) is different? Sometimes textbooks have the wrong answer for problems.

The answer I get is:

I1 = 2.69767
I2 = 1.93023

Alright thanks, looks like the answer in my textbook is wrong.

 

[SpartanG345]

just wondering what text are u using?

 

[ammontgo]

2 Equations & 2 Unknowns.
My Equations

Mesh 1:
[PLAIN]https://dl.dropbox.com/u/4645835/MATH/mesh1.gif

Mesh 2:
[PLAIN]https://dl.dropbox.com/u/4645835/MATH/mesh2.gif

 

[ejk5401]

Why do you think your answer is wrong? Is it because the answer given by the textbook (or your instructor) is different? Sometimes textbooks have the wrong answer for problems.

The answer I get is:

I1 = 2.69767
I2 = 1.93023

I never said you were wrong, I shown him how to apply mesh anly so he could use it in the future. if you notice i didn't give an answer ;)