# Lab 4

#### xswtxoj

1. The problem statement, all variables and given/known data

well first its to plot the graph ( volt vs. current) then determine the effective resistance of the two resistors in series. 2nd compare the effective resistance of the resistors in series with the resistances of each resistors.

2. Relevant equations

R=V/I

3. The attempt at a solution
Based on this chart: then graph
Voltage (Volts) Current (Amps)
3.24 .021
9.32 .060
14.67 .095
20.3 .123
8.2 .056
15.4 .106

R= V/I 3.24/.021 = 154.3
15.4/.106 = 145.3

Last edited:

#### Tom Mattson

Staff Emeritus
Gold Member
Compare the effectiveness resistance of the two resistors in series of each resistor
That sentence makes no sense at all. Can you please carefully type out the problem exactly as it appears in your lab handout?

#### djeitnstine

Gold Member
I assume you mean "effective resistance of 2 resistors in a series circuit" in which case you simply add them up

#### Tom Mattson

Staff Emeritus
Gold Member
Sure, that's how you compute them. But the OP says compare. What is he supposed to compare them to?

#### xswtxoj

well first its to plot the graph ( volt vs. current which i did) then determine the effective resistance of the two resistors in series. 2nd compare the effective resistance of the resistors in series with the resistances of each resistors.

Last edited:

#### Tom Mattson

Staff Emeritus
Gold Member
OK, so do you know how to get the effective resistance from the plot of voltage vs current?

#### xswtxoj

pick 2 coordinate points and find slope, where slope = R

#### Tom Mattson

Staff Emeritus
Gold Member
I wouldn't just pick 2 points, but rather the best line that fits all of the data. If you haven't learned about that (linear regression that is) then I would just compute the resistance for each data point and then average them. That will be the effective resistance.

#### xswtxoj

can u pick 2 point from graph on the line and find slope? then once you find the effective resistance, then compare the effective resistance of the resistors in series with the resistances of each resistors?

#### Tom Mattson

Staff Emeritus
Gold Member
Like I said, I wouldn't pick just two points. If you do that then you aren't taking all of the data into account.

#### xswtxoj

but in general to find resistance using ur data points do u do V/I = R or v2-v1/I1-i2 for a single resistor?

#### Tom Mattson

Staff Emeritus
Gold Member
Only if you have 2 data points. If you have more then they must be included somehow.

#### xswtxoj

If I have this
Data Table 2: The Voltage vs. Current for a Single Resistor Circuit
Current V
0.01 0.5
0.02 0.8
0.03 1.3
0.04 1.8
0.05 2.3

then would i calc. (2.3- 1.3)/ (.05-.03) = 50

#### Tom Mattson

Staff Emeritus
Gold Member
Can't you see that if you use only those two data points that you're ignoring the rest of the data?

#### xswtxoj

so i have to calculate each indivudual points?

#### Tom Mattson

Staff Emeritus
Gold Member
I said that 8 posts ago.

#### xswtxoj

Resistances

1. The problem statement, all variables and given/known data

well first its to plot the graph ( volt vs. current)
then
1. determine the effective resistance of the two resistors in series.
2nd compare the effective resistance of the resistors in series with the resistances of each resistors.

2. Relevant equations

R=V/I

3. The attempt at a solution

Based on this chart: then graph
Voltage (Volts) /Current (Amps)
3.24 /.021 =154.3
9.32 /.060 = 15.53
14.67 /.095 = 154.4
20.3 /.123 =165.0
8.2 /.056 =146.4
15.4 /.106 = 145.3

I divided (v/I = r)

so far I dont know how to continue.

#### Tom Mattson

Staff Emeritus
Gold Member
I've merged your two threads. In the future please do not start multiple threads for the same question. It is not necessary and is considered spam.

so far I dont know how to continue.
I told you exactly how to continue in Post #8.

#### xswtxoj

so for series i calculate each individual then add all the R's and get the average, is it the same for parallel too?

#### Tom Mattson

Staff Emeritus
Gold Member
Yes, I would do the same for parallel resistance.

### The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving