Theory:

According to the Ohm’s Law, the current passing through a wire at constant temperature is proportional to the potential difference between its ends. Ohm’s Law applies just to the metallic conductors. In my particular experiment there are two variables I’m going to control, which can affect the resistance in the wire. Here I want to describe how exactly it can affect the resistance and the reason why. First of all, thickness SWG (standard wire gauge), or how it is also called cross sectional area. If the area is very wide, it will allow a high current through it, while a narrow area would be difficult to get through due to it's restriction to a high rate of flow. A conductor with a larger cross section area allows more electrons to interact with the field. Conductor with a larger cross section area has lower resistance. Therefore, the resistance is less in a wire with a larger cross sectional area. The resistance of a wire is inversely proportional to a cross section width. If the area/cross section of the wire is doubled, the resistance will be halved. The length of a wire is the second variable in my experiment which can also affect the resistance. It is similar to a hallway. A shorter hallway allows people to move through at a higher rate than in a longer one. In order explain it in more details; I decided to provide a picture, which s hows how it actually happens.

On this particular picture, we can’t see a shorter hallway. But it shows that more electrons can get through a thicker wire rather a thinner one, especially when a thicker wire is short. This allows more electrons to get through at a quicker time. Therefore, a shorter wire allows electrons to move at a higher rate than in a longer wire, causing less resistance. Type of the material is very important as well. Different materials have different resistances. Different type of the wire used can have a different affect in the resistance of the wire in my experiment. Therefore, it will be better to do a trial experiment and try different types of the wire to find an optimal piece with a relatively high resistance.

Prediction:

According to the Ohm’s Law I predict, that in my experiment the resistance of the wire will increase in proportion to length. As the length of the wire increases, less electrons can pass through the wire and, therefore, the resistance of the wire increases. As the thickness of the wire increases, the resistance will decrease. I also predict that when the current increases, the potential difference in the circuit will decrease, or in other words, the potential difference will be inversely proportional to the current. In order to make it more clear and easy to understand, I decided to plot two graphs which show exactly how I predict, the resistance is going to change.

Method

First of all, I’m going to do a trial experiment, which will help me to choose the right piece of the wire and optimal length. I’m going to set up a circuit, with the power switched off, as shown below.

Then I’m going to cut and try different pieces of the wire of the same length, 30cm. I’m going to try Eureka 26 SWG, Constantan 34 SWG and Nickel Chrome 30 and 34 SWG. Then I’m going to choose the right wire, which I decided to be a Nickel Chrome one with 34 SWG. After that, I’m going to start my real experiment, where I’m going to investigate how the length affects the resistance in a particular type of the wire. I’m going to set up a circuit as I did in my trial experiment. Then, I’m going to cut 60cm of the Nickel Chrome wire, which I chose to be the best one. Actually, in my experiment I’m going to use just 55cm of the wire, but in order to make it more accurate, I chose to cut 60cm and make sure that I put the crocodile clips exactly at two points 0 and 55cm. As I change the length of the wire, I’m going to decrease it by every 5cm beginning from 55 to 20 cm. In my experiment we are going to work in pairs, so while I’m fixing the crocodile clips, my partner is going to take the readings from the voltmeter and ammeter. After I fixed the crocodile clips on the wire with a power supply on, I wait I’m going to tell my partner to take the readings. Then I’m going to put the crocodile clips closer, wait till my partner is ready and tell him to take the readings again. Then we are going to calculate the resistance, using a formula: R=V/I or (Resistance (Ω) = Voltage (V) / Current (I)). When we finish this, we are going to repeat the whole experiment again, where I will be taking the readings and my partner will be fixing the crocodile clips on the wire. After we finish this procedure, we are going to calculate the resistance in the second experiment and, if we are satisfied by the results gathered, we are going to put them in the results table and begin plotting a graph and its analysing afterwards separately from each other.

Results

Results for the trial experiment

Type of the wire	Thickness (SWG)	Length of the wire (cm)	I (A)	V(V)	R(Ω)
Eureka	26	30	3.15	2.31	0.73
Nickel Chrome	30	30	1.03	4.4	4.34
Constantan	34	30	1.12	4.33	3.87
Nickel Chrome	34	30	0.61	4.81	7.90
Nickel Chrome	34	15	1.07	4.35	4.05
Nickel Chrome	34	20	0.81	4.53	5.59
Nickel Chrome	34	25	0.57	4.67	8.19
Nickel Chrome	34	30	0.56	4.69	8.40
Nickel Chrome	34	35	0.36	4.84	13.4
Nickel Chrome	34	40	0.41	4.69	11.44
Nickel Chrome	34	45	0.38	4.72	12.42
Nickel Chrome	34	50	0.34	4.74	13.94
Nickel Chrome	34	55	0.28	4.75	16.96