Science Report Help

Discussion in 'Homework Help' started by Sharie, Feb 26, 2012.

1. Sharie Thread Starter New Member

Feb 26, 2012
3
0

Ohm's Law - Resistance?

Below are the results of an experiment I did at school to determine the resistance of an unknown resistor. The results are all over the place and I am having difficulty explaining what went wrong.

The Resistor's actual resistance was 2.2 ohms, but the results were considerably different. I need to explain the results and if the percentage errors are acceptable, but I am having trouble understanding all of this.

1. Can someone please explain why these results likely occurred (errors in the experiment)?, and;
2. Are there any relationships between the results I should highlight (like the amps dropping as the resistance increases in Trails 3 and 4 where the voltage is constant)?

Trial Current (Amps) Voltage (Volts) Resistance Percentage Error:
1 0.74 1.5 2.027 -7.863%
2 0.82 1 1.2195 -44.5681%
3 0.2 0.5 2.5 13.53%
4 0.14 0.5 3.5714 62.336%

2. justtrying Senior Member

Mar 9, 2011
330
891
whether the percentage errors are acceptable depends on the tolerance of your resistor. If it is 10% (most often used for experiments), then you have one good trial and 13% is not that bad. But now you have to think what may have gone wrong. Notice how there is hardly any change in current btw trials 1 and 2 and none at all between trials 3 and 4, I find that curious. Think over how you carried out the procedure.

3. Sharie Thread Starter New Member

Feb 26, 2012
3
0
Thank you ofr your answer. Unfortunately, I was away the day the experiment was conducted by my group and I only have their notes to go on. So, Trials 1,2 and 4 are way off the mark basically? So very little change in the voltage would be a result of the Rheostat, which we adjusted slightly after each Trial?
Thanks again for your help - just need to be pointed in the right direction with this. I've done so much reading, but have only managed to confused myself.

4. Sharie Thread Starter New Member

Feb 26, 2012
3
0
Sorry for the terrible spelling. I have been reading and typing all day. The group said they only slightly adjusted the rheostat after each trial, but could adjustments have caused such significant differences in the results?

5. justtrying Senior Member

Mar 9, 2011
330
891
Actually, I am re-reading your data, in trials 3 and 4, was voltage changed at all? it looks like voltage is 0.5 in both yet current changed, that just cannot happen...

Your group used rheo. to adjust voltage and then measured current through the resistor. The other thing to ensure is that correct voltage was measured (i.e. voltage drop across the resistor) - discuss it with your group since you were not there.

6. JoeJester AAC Fanatic!

Apr 26, 2005
4,018
1,772
Maybe it would help if you posted the lab proceedure used ... complete with schematic.

That would give us a clue of what the lab's objectives and could illuminate on what your lab mates may have done to produce the results.

7. BillB3857 AAC Fanatic!

Feb 28, 2009
2,477
382
When dealing with very low resistance values, even the length and size of the connecting wires can introduce errors. The leads on my digital VOM measure about 0.2 ohms with the test probes shorted.