In place of repeats we decided to measure three measurements of voltage (2v, 4v & 6v) at each metre. This way we making our results more accurate, without having to repeat the whole test again.
Changing the voltage shouldn’t affect the resistance; the relationship should be the same because of V = I ✕ R. This is Ohms law.
Ohms law states that the current through a conductor is proportional to the potential difference (Voltage).
(V= Voltage (v), I= Current (A), R= Resistance (Ω))
Once our results have been obtained, we will need to rearrange the formula V = I ✕ R, so that we can find the resistance. Therefore we will use the formula R = I ÷ V
To keep the investigation safe we are going to turn off the power pack between each reading to stop the wire from burning and stop us from burning ourselves We will also keep safe by not increasing the voltage more than 6v.
Method
1. Lay down the 6m-length wire flat on the floor; make sure it is taught so there are no kinks or knots.
Using a 1m-ruler measure out 1m at a time using masking tape to mark where each metre begins and ends.
2. Secure the wire on the table with masking tape; still making sure of no kinks or knots.
3. Set up the equipment as in diagram above.
4. Switch on the power pack at 2v and take readings from the voltmeter and ammeter at 1m on the wire, then switch off the power pack.
5. Repeat step 4. Changing the voltage to 4v and then repeat again for 6v.
6. Repeat steps 4 & 5 but changing the length to 2m and then 3m, 4m, 5m and 6m.
7. Remember to switch off the power pack between each reading, otherwise the wire will burn.
My results
Having performed the investigation the following conclusions were made:
As predicted when the length of wire increased the resistance also increased. This can be clearly seen from the graph. The trend on the graph is a straight line, which proves that the relationship between the resistance and the length is proportional. This also proves what I know of Ohms law, that V = I ✕ R and that the current and voltage are proportional to each other.
The resistance increased with the length because as the wire gets longer it makes it harder for electrons to flow down. As the wire length increased the number of free electrons also increased, which means that more electrons collided with the static positive charges (protons), causing them to lose energy and therefore making it harder for the electrons to flow.
Overall I think the procedure we used went well. The evidence we collected was what I originally predicted. However there were a few that stood out on our graph and table of results. At 5m we had the results 72 at 2v, 61.6 at 4v and 59.38 at 6v.
These results are strange because they the difference between them is quite big, when compared to the results for 1m. The difference between them shouldn’t be so big because the Ohms law states that the relationship between current and voltage is proportional.
Possible explanations for these anomalies are, for example,
- We might not have switched off the power pack long enough for the wire to cool as much as the measurement before. This would affect our results because the hotter a conductor is, the more resistance it has.
- Another factor that could have affected it is the length. Our measurements might not have been as accurate at that particular metre.
With the exception of one anomalous result I think that our results are quite accurate, as they are what we expected, and I think that we can use this evidence to support a firm a conclusion. We can also see that the quality of results and evidence is good.
If we were to do the investigation again more accurate results could be obtained by using more accurate equipment. While using the school equipment is was sometimes hard to write down an accurate result as the ammeter and voltmeter kept changing it’s reading. In the end we had to take the result that the ammeter or voltmeter flickered to the most. This is not an accurate way to record quality results.
We could also get more accurate results by doing more repeats. That way we could a more accurate average of the resistance and identify more anomalous results.
Overall I think that my results are good enough to support my prediction and my conclusion.
