Table 2:
Procedure:
- Take 5 copper wires of different diameter (same length), and 4 of different length (same diameter). Label them with numbers 1-9.
- Set up the circuit diagram as shown in the diagram below.
- Set the range of the voltmeter in “0-20V”, and set the range of the ammeter in “0-20A”
- Connect wire number 1 in the circuit.
- Record the current and potential difference across the wire.
- Record the values for current and voltage in the table.
- Repeat step number 4 and 6 until finish with all wires.
Data processing and conduction:
Form the formula I=, we can know R=, so when we calculate the resistance, just put the values of Voltage and Current into the formula. The way to calculate the area of wires’ cross section is π()2.
Table 3:
Because of, and the length is constant. So I will those figures to draw a graph. The x-axis is the area of wires, and the y-axis is the resistance.
Table 4:
Because of, and the diameter is constant, so the area of the wires’ cross section is constant also. So in this diagram the x-axis is length and y-axis is the resistance.
From the graph, we can see the relationships between resistance and area when use the same length wires and relationship between resistance and length when use the same diameter wires. So, we can know the resistance and area/length of the wires are in direct ration.
When the length is constant, the average resistance is 0.55(3.m.f), average current is 3.5A, and the length is 2.5m. So we can use the formula, is variable, so the gradient of the curve is equals to7.737×10-8, so is equals to2.95×10-8Ωm The criteria value of the resistivity is, so our experiment error is 70.6%.
When the diameter is constant, it means the area of the conductor is constant as well. It is equals to1.46×10-7m2 . The average resistance is 0.268Ω. So use the formula, is variable, so is equals to1.3×10-8Ωm. The criteria value of the resistivity is, so our experiment error is 23.5%.
Skills:
Manipulative skill: When we change the wire to do the experiment, we must turn off the power first. And we could keep connected for long time, because we keep connected that time, the electron and atom never stop collided, kinetic energy transferred to heat energy, so it will take out a lot of quantity of heat. So if long time, it is too hot.
Personal skill: While I doing the experiment, we found the ammeter could work, we change the ammeter, it is still happened. And then we check the connection, all are at good conditions. So we try to use sand paper rub the face of the tinsel. But the ammeter stills no reaction. So at least we change the wire to other same dimension wire, the lucky is the ammeter worked.
Errors:
Systematic errors:
When we first start using the ammeter and voltmeter, a zero error may occur. This will lead to wrong readings, causing more percentage error. So you can restart it, if still happened, check how much errors more or less. So after see the data on meter, ensure that you minus or plus back the value to the readings, to get a more accurate readings.
Parallax error:
We must measure the data quickly, because if the wire keeps connected so long time, the temperature will increase. The data will become incorrect.
Ways to decrease percentage error:
- When using the copper wire as a conductor for this experiment to find out the resistivity, make sure that there is no rust on the wire, the rust can affect the current pass it. So, before use the copper wire. We must use sand paper to rub two sizes of the wires. This is to make sure a better and a more accurate reading.
- We must make sure all the wire connected completely, if not, the figure of the meter will always change.
Conclusion:
From the experiment we can see: the first experiment is when the length is constant, the experiment of that error is 70.6%. The figure is much bigger that normal. So I think is the errors I shown above happened, so the experiment is so much. The second experiment is when the diameter is constant, the experiment of that error is 23.5%, the figure is not so difference as normal, but still have experiment error, I think why this like this is: the room temperature is changed, so the resistance is change. And the other wires also have resistance, but we couldn’t calculate it.