Kirchoffs Law (again)

Thread Starter

Dazedandconfused

Joined Nov 5, 2020
2
Morning all,
And apologies as I imagine this has been done to death, but I’m on my assignment for a HNC done via distance learning and I’m struggling with the attached Kirchoffs law equation. I’ve got this far, which I think is correct but I’m genuinely stuck now.
could anyone point me in the right directions for the next few steps?
thanks in advance.
 

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dl324

Joined Mar 30, 2015
12,668
could anyone point me in the right directions for the next few steps?
Don't use color coded schematics.
clipimage.jpg
Ask a specific question instead of making us try to follow your logic in the equations. For starters, your loop equations would make more sense if you didn't jump around in the loop.
 

WBahn

Joined Mar 31, 2012
26,398
Morning all,
And apologies as I imagine this has been done to death, but I’m on my assignment for a HNC done via distance learning and I’m struggling with the attached Kirchoffs law equation. I’ve got this far, which I think is correct but I’m genuinely stuck now.
could anyone point me in the right directions for the next few steps?
thanks in advance.
Please explain where the '16' comes from in your second loop equation.

You really need to start tracking your units properly.

At the end you have two equations in two unknowns. Do you not know how to solve for the unknowns? If not, that's a math issue and you need to spend some quality time with some algebra texts or websites to build up those skills.
 

Thread Starter

Dazedandconfused

Joined Nov 5, 2020
2
Please explain where the '16' comes from in your second loop equation.

You really need to start tracking your units properly.

At the end you have two equations in two unknowns. Do you not know how to solve for the unknowns? If not, that's a math issue and you need to spend some quality time with some algebra texts or websites to build up those skills.
I think, it's possibly a combo of the 'maths' and understanding the actual formula/law to be honest. I think because the course is a 'distance learning' all done over Zoom, it's quite difficult to follow if things don't quite make sense.

The 16 = V2 (8V) x R2 (2ohms)

I believe If I multiply equation 5 into equation 6 that will give me the final formula I need (barring multiplying out the denominators) but I'm not quite certain.

I1 + I2 = I3 - eq1

Loop 1 –

12-8 -V1+V2 >>> 4= V1-V2

4= 1/10I1 -2I2 eq2

Loop 2 –

16= V2+V3

16=2I2+1/7I3 eq3

16=2I2+ I1 + I2 eq4

CCT –

4=1/10 I1-2I2 eq5

16= I1+3I2 eq6
 

WBahn

Joined Mar 31, 2012
26,398
I think, it's possibly a combo of the 'maths' and understanding the actual formula/law to be honest. I think because the course is a 'distance learning' all done over Zoom, it's quite difficult to follow if things don't quite make sense.

The 16 = V2 (8V) x R2 (2ohms)

What do you get if you multiply a voltage, 8 V, by a resistance, 2 Ω?

You do not get 16. Nor do you get any kind of voltage, current, resistance, or power.

That is why I told you that you need to properly tract your units. Otherwise exactly what happened here will happen to you over and over again. Your loop equations are were all of the physics happens; everything after that is just math. If your set up equations are wrong, then all the correct math in the world won't lead to a correct answer.

If you track your units properly, then when you make mistakes like this you can spot them immediately and not waste a bunch of effort slogging through work that is only guaranteed to lead to a wrong answer.

Had you carried your units, you would have

16 VΩ = V2 + V3

and it should have stood out that this is not possible because the units don't work. So you would then have the opportunity to profitably take a step back and ask why the units don't work instead of blundering right ahead on a fool's quest.
 
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