Where R = resistance
V = Pd. Across the conductor
I = current
This formula will give me a result in Ohms.
Apparatus:
Ammeter - 0-5 Amperes
Voltmeter - 0-5 Volts
Wires - insulated
Bare wire - 1.6mm, and lengths of 10cm 20cm 30cm 40cm
Power supply - AC, 0-5 volts
Circuit:
My circuit is set up to produce accurate results; the ammeter is in series so all of the amps travel through the ammeter. (It would reduce the number of amps if it were in a parallel circuit because some of the amps have to travel along the other wire).
The voltmeter is in parallel with the wire because the volts are equal across the circuit when in parallel.
I will measure:
Volts - voltmeter
Amps - Ammeter
Temperature - close watch on wire (keep voltage low)
Resistance - Formula (R=V/I)
Prediction:
I think that the longer the wire, the more resistance, because electrons lose some of there energy when they collide.
I will keep the voltage low to minimise resistance. This is due to kinetic theory, the more voltage, the hotter the wire, the faster moving particles therefore the more energy lost through collisions.
The graph will be a straight line through the origin, because current is proportional to the voltage, hence the resistance I=V is constant, showing that the wire is an ohm conductor.
I also predict that resistance will be proportional to length, I predict a length of wire 10cm long will have twice as many collisions as a wire 5cm long.
Results:
Length (cm) Voltage (volts) Current (amps) Resistance (ohms)
5 4 2.26 1.7
10 4 1.76 2.2
15 4 1.56 2.5
20 4 1.33 3
Analysis:
The results I found were expected because the results were proportional to each other. From the graph I can see that the resistance of the wire is proportional to the length of the wire. I know this because the Line of Best Fit is a straight line showing that if the length of the wire is increased then the resistance of the wire will also increase.
Conclusion:
I conclude that, as the length of a wire doubles, the resistance also doubles (provided the thickness of the wire is kept constant). From my graph I have shown that my prediction was correct, as the Line of Best Fit is a straight line proving that the resistance of the wire is proportional to the length of the wire.
The length of the wire affects the resistance of the wire because the number of atoms in the wire increases or decreases as the length of the wire increases or decreases in proportion. The resistance of a wire depends on the number of collisions the electrons have with the atoms of the material, so if there is a larger number of atoms there will be a larger number of collisions, which will increase the resistance of the wire. If a length of a wire contains a certain number of atoms when that length is increased the number of atoms will also increase.
The way I got my results was fair; I controlled temperature, voltage, length of wire, and the resistance in the circuit.
My results were all accurate; I did not get any anomalous results at all because I took more than one result and calculated the average, this increased the reliability of my results. But using a variable resistor would create even more accurate results. By checking my results with formulas from text books it proves my results are accurate enough to support a firm conclusion that resistance is proportional to the length of the wire. To improve the experiment I could use different thickness´ of wire, different materials of wire or use a variable resistor.
