Determine the effective resistance of the two resistors in series

[xswtxoj]

Homework Statement

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.

Homework Equations

R=V/I

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

 

[quantumdude]

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]

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

 

[quantumdude]

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.

 

[quantumdude]

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

 

[quantumdude]

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?

 

[quantumdude]

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?

 

[quantumdude]

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

 

[quantumdude]

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?

 

[quantumdude]

I said that 8 posts ago.

 

[xswtxoj]

Resistances

Homework Statement

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. Homework 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 don't know how to continue.

 

[quantumdude]

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 don't 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?

 

[quantumdude]

Yes, I would do the same for parallel resistance.

 

[xswtxoj]

compare the effective resistance of the resistors in series with the resistances of each resistors. I used resistors 47 and 100, and for series I got 153 and parallel was 31.4, does that indicate that series is more capatible with resistor 100 and series is with resisotr 47?

 

[quantumdude]

When they ask you to compare two resistances they mean for you to state which resistance is greater.

 

[xswtxoj]

I don't quite understand what this means, show the experimental and theoretical calcs. for the resistance of the series/parallel. If i have the measured series as 146.7 and 31.7 as parallel, and the total equivalent resistance is 47 & 100

 

[quantumdude]

The experimental calculation is what you got by averaging the resistances from each individual data point. The theoretical calculation comes from plugging the values of the single resistances into the formulas for series and parallel resistance.

 

[xswtxoj]

for the parallel series, adding the r's will be 1/r? also determining whether or not ohm's law is obeyed in this experiement is where the graph is showing a growth trend?

 

[quantumdude]

for the parallel series, adding the r's will be 1/r?

Weren't you taught a formula for adding resistors in parallel?

also determining whether or not ohm's law is obeyed in this experiement is where the graph is showing a growth trend?

More specifically, the voltage should grow linearly with current. Ohm's law is the equation of a line with slope R in the v-i plane.