Question

anyone good with excel? how do i do this in excel? example of what this looks like would be helpful.

Answer 1

You are given the values to calculate your current drops. Place your knowns within a cell, then use your formula editor in excel to create the math you need.

Answer 2

Assuming a series circuit with 3 resistors, your excel would look something like this. You shouldn't have any problem applying this example to your circuit.
Good luck and let us know if you get stuck.

Answer 3

@eSpeX How do I use goal seek for this equation?

Answer 4

@agent0smith

Answer 5

@Ash90 Give this tutorial a look, it should be a simple task to adjust it to your needs. http://office.microsoft.com/en-ca/excel-help/use-goal-seek-to-find-the-result-you-want-by-adjusting-an-input-value-HP010342990.aspx

Answer 6

i'm trying to do that step and for some reason my math solver is in error.

Answer 7

@eSpeX i don't know what it is i'm doing incorrectly.

Answer 8

i've been trying to get this right for 2 hours now and i'm still stuck because it has errors in it.

Answer 9

that's what i have so far and when i tried using solver or goal seek i would get an error

Answer 10

I'm sure you could solve this circuit using Excel, but I haven't thought about doing it that way. Unless you're REQUIRED to use Excel, why not treat the 3 given equations as a set of 3 equations in 3 unknowns and proceed to solve the system using one of the following methods:
1. substitution
2. elimination by addition/subtraction
3. matrices
4. determinants.

Answer 11

I have an idea of what "Goal Seek" is, but have not actually used that on Excel yet.

Answer 12

yeah it's required for us to use excel. As for using sub, elimination or matrices etc. i'm not sure if he'll allow that he is very strict. but i might try it.

Answer 13

I would, in your shoes. If you succeed, then you'll have a solution to compare to a solution obtained through Excel.

Answer 14

Using matrices on my TI-83 Plus calculator, I was able to solve this system for the three different currents. \[i _{1}=\frac{ 27 }{ 130 };~i _{2}=\frac{ 9 }{ 130 }\]

Answer 15

I'll leave it to you to verify these and to find i3.

I've re-read your problem statement and see that you do need to use Excel. surely wish I were more familiar with that Solver or Goal Seek utility.

Answer 16

Sorry for not responding right away. I will certainly try this and see what I get.

Answer 17

okay @mathmale for i3 i get 9/65 still having trouble with excel's solver.

Answer 18

@Ash90 I created the page with the same values that you did. I then opened the Goal Seek and picked the cell for i2 ($B$8 in my case) that had the formula I=E/R, then picking the value that I wanted to get, a current from 0.3A to 1A, and finally choosing the value I wanted to adjust (I chose increasing the voltage so $E$3). Goal Seek then calculated that a voltage of 30 was needed to get the 1A I was after for i2.
What exactly is the error you are getting?

Answer 19

@Ash90 Looking at your sheet a little closer, I notice that you have no values populated in B41 - B43. These cells should have the formula "=E36/B36, =E36/B37, =E36/B38" respectively, perhaps therein lies your error.

Answer 20

i'm not surei f i'm putting them in correctly @eSpeX

Answer 21

i don't know what to put in for the set cell, value and change cell to find both i1, i2, and i3?

Answer 22

Alright, looking at your sheet the formulas all look right. Now let's try something using "Goal Seek".
Select cell B43 (i3) then click on the Data tab, then What-If Analysis, then click on Goal Seek.
The Goal Seek window will come up with "Set cell:" already populated with B43. Now let's say we want to know what it would take to get 0.5A on i3 (B43). We enter 0.5 in the "To value:" text box. The last step is to "change something", so we want to know what size of resistor R2 would need to be in order to give us that 0.5A on i3. Highlight the "By changing cell" box and select B37 (R2). When you click "OK" you will see the numbers flicker as it tries various combinations, only to ultimately fail as there is no value of R2 that will give 0.5A on i3.
Now you can try it with different combinations, like try changing the voltage instead of a resistor.

Answer 23

when i did that i got i2 -8.9e-07 and r2 -1e+07

Answer 24

Yes, and if you look at the Goal Seek window you will see that it failed. Try an example that will work, select i1, then Goal Seek, then set your change to value to 1, then tell it you want to change the voltage.

Answer 25

alright. thanks. I'm finally starting to know how to use this thing lol.

Answer 26

You're welcome. Good luck.