# Graphing Resistance vs. Bandwidth, why wouldn't go throught the origin?

1. Oct 30, 2008

### crh

I am using Excel and plotting a line of best fit for Resistance vs. Bandwidth. I used the LINEST function to get my values, and it shows that it would cross the y-intercept at around 288 Hz. I am just wondering why when using resistance vs bandwidth it would never cross at the origin. That is what my manual says, and I guess that I am just confused as to why they could both never be zero at the same time. Am I over thinking this, could someone just clarify it for me.

2. Oct 30, 2008

### Redbelly98

Staff Emeritus
Two possible reasons come to mind:

1. The scatter in the data produces a best-fit line that is close to, but not through, the origin.

2. The data consists of points relatively close to each other, but far away from the origin. So a small amount of scatter in the data produces a best-fit line that is not even close to passing through the origin.

Without seeing your data, it's impossible to give a definitive answer. You haven't told us any details about the system or circuit being measured. If the bandwidth data are in the MHz range, then 288 Hz is for all practical purposes at the origin.

3. Oct 30, 2008

### crh

R(x) BW(y)
50 457
100 636
200 937
300 1296
400 1614
500 1938
600 2290
800 2925
1000 3630

LINEST function:
3.322306649 288.8765265
0.016948199 9.025789158
0.999817868 15.33684586
38426.63043 7
9038667.468 1646.531886

This is my data. I know that as resistance increases, bandwidth increases. I get the relationship between the two. I just don't understand that no matter what, when I graph them that it would never go through the origin. My manual says that no matter the numbers it would never be y=0, x=0. I guess I just can't understand why.

Last edited: Oct 30, 2008
4. Oct 31, 2008

### Redbelly98

Staff Emeritus
I plotted your numbers in Excel, and you're right it clearly does not go through the origin. There is very little scatter in the data and it produces a nice straight line.

I don't know anything about what you're actually measuring, but it might be that your measuring instruments contribute to the bandwidth. If so, then even when resistance=0 there will be a measureable bandwidth due to the instrumentation.

Realize that I am merely guessing, since you haven't described your experimental setup.