Resistance of a Wire

Physics Coursework

Objective:

My objective in this experiment is to investigate one of the factors that affect the resistance of a piece of wire; the one I am investing is the length at constant temperature.

My objective in this experiment is to investigate one of the factors that affect the resistance of a piece of wire. The factor I chose was length.

Factors:

There our four different things that affect the resistance of a wire:

1. The Length - because the wire is thinner than the rest of the wires the electrons wood have more trouble going through for if the wire had the same width there would be no difference, and the longer it is the harder it will be for them so the resistance will go up.

2. The Width - when the wire is very thin its very hard to go through, you can compare it to a person going through a big, or little door, the thinner the door (wire) the harder it will be to go through it. With other words the thinner the wire gets the higher the resistance.

3. The Temperature - when the wire gets warmer and warmer the metallic ions will vibrate more and more making it harder for the electrons to move, just like when you're in a room with dancing people. The higher the temperature the higher the resistance.

4. The type of Metal - the type of metal has everything to do with the resistance, because some metals have looser electrons then others the can go around faster. And because the electrons can move fast they can flow through the wire fast, meaning that the resistance will be lower.

Prediction:

I think that if you ad more length to the wire it will be harder for the electrons to go through because, they all should have to have a longer way threw a small 'tunnel' making it harder for them to pass the tunnel. I also think that the wire at constant temperature shall be an ohmic conductor.

I predict that the longer the wire, the more resistance. This would be because the more distance that is covered while going from point A to point B, the more time that would be taken, and therefore the more resistance. Therefore, the shorter the wire, or the less distance for electrons to travel, the less resistance.

Plan/Procedure

In this experiment I shall start of by making a diagram (see image 1) with the following stuff:

Wires

Ammeter

Voltmeter

Light bulb

Power Pack

Variable Resistor

Special wire (in different lengths)

First I started with the longest measurement, 100 cm. I placed the wire so that it connected to the ammeter, voltmeter and light bulb. The light bulb was used so we could tell that the connection was correct (it would light if the circuit was connected properly). After connecting everything as the diagram shows, we turned on the power pack so that a flow of electrons could be sent around the circuit. I set the variable resistor so that the readings on the voltmeter and ammeter wouldn't run off the numbers shown. Then, I recorded the readings on the voltmeter and ammeter. Since the voltmeter was set to 3 volts, those recordings were all the same. To work out the resistance, I divided the readings on the ammeter by the readings on the voltmeter for each length.

First I shall set up the circuit (see image 1). Then I shall start of with a wire which has a length of 100 cm and read the volts and current by looking at the volt + ammeter, with that information I shall use the equation from Ohm's law to figure out the resistance. This I shall do a couple of times each time subtracting five cm off the wire. I shall also look at the light bulb and see if its getting brighter for it is supposed to (because the resistance get lower for each five cm that the wire looses). To make sure I do it right I shall calculate the resistance of one cm wire by dividing the resistance by the length now if I multiply that by one hundred it shall show me how high the resistance should be if the wire was one hundred cm long, all these answers should be round the same. If that is true I am doing the test success fully. I shall also make sure the wire stays at constant temperature for if the electrons start vibrating more and more by the energy it is getting from the temperature the harder it will be for the current to flow through making the resistance go up as well and we don't want that. This is because we only want to show how the length affects the resistance and not length + temperature. Once I have the full sets of results I shall plot them in a graph and say what I learned.

Results:

Test 1:

Lengths (cm) Ammeter (amps) Voltmeter (volts) Resistance (ohms) Resistance per unit length

(ohms/meter)

100 0.34 3 8.8235 8.82

95 0.36 3 8.3333 8.77

90 0.38 3 7.8947 8.77

85 0.40 3 7.5000 8.82

80 0.42 3 7.1429 8.93

75 0.44 3 6.8182 9.09

70 0.48 3 6.2500 8.93

65 0.52 3 5.7692 8.88

60 0.60 3 5.0000 8.33

55 0.64 3 4.6875 8.52

50 0.72 3 4.1667 8.33

45 0.78 3 3.8462 8.55

40 0.88 3 3.4091 8.52

35 1.00 3 3.0000 8.57

30 1.20 3 2.5000 8.33

25 1.40 3 2.1429 8.57

20 1.70 3 1.7647 8.82

15 2.30 3 1.3021 8.68

10 3.46 3 0.8681 8.68

5 6.91 3 0.4340 8.68

(for graph see last page)

The last three measurements are not actual measurements. When we took the measurements we saw that something went wrong that we couldn't figure out, so we discarded the measurements. The values