Results

GCSE Physics coursework

How the length affects the resistance in the wire.

Plan:

· Introduction

· Aim

· Equipment

· Controlled variables

· Accuracy

· Theory

· Prediction

· Method

· Results (Results table and graph)

· Analysis

· Further investigations

· Evaluation

Introduction

The purpose of this investigation is to expose the factors responsible for affecting the resistance of a wire in an electrical circuit. Many factors will have to be investigated before I start a real experiment. Resistance occurs when there’s a substance, which can resist the flow of electricity which goes through it.

Resistance depends on many factors, such as:

• Type of the material
• Its temperature
• Dimensions, and thermal properties
• The surface
• Frequency and magnitude of the current.

Aim

The aim of this experiment is to investigate how the length affects the resistance in the wire. I will be measuring the voltage and current, which are going to go through the wire. According to the results I get, I will be calculating the resistance of the wire. Whilst varying the length of the wire, I will be recording all the changes, which occur in the wire. After that, I will be able to plot the graph and investigate how the length affects the resistance in the wire. Although, I will be measuring the resistance in the wire and investigating the factors, which affect it, I also need to produce reliable evidence, which will prove my prediction was right. In order to prove it, I will need to link my evidence to the scientific knowledge. In my particular experiment it is going to be the Ohm’s Law, which basically says, that the current passing through a wire at constant temperature is proportional to the potential difference between its ends. Therefore, I will be investigating and trying to prove that this law relates to my particular experiment.

Also, in my particular experiment I’m not going to control all the variables, such as temperature of the wire, dimensions, thermal properties, magnitude of the current and etc. Of course there are some reasons for that. It is very difficult to measure some of these variables, and they also don’t relate to the question and aim of my experiment. In my experiment there will be following controlled variables, which I will be controlling and changing during the experiment.

Controlled variables:

· Type of the material (Types of the wire)

· The supplied voltage (will be hopefully kept the same during the whole experiment)

· Thickness of the wire (SWG)

Equipment:

· Ruler (100cm)

· Piece of Nickel Chrome wire 60cm long (this particular type of wire will be constantly used only in the real experiment)

· Scissors

· Battery Power Supply

· Voltmeter

· Ammeter

· Crocodile clips

· Calculator

Accuracy:

First of all, I’m going to keep a fair test. Therefore, I’m going to make sure I use the same material, thickness, and type of the wire during the whole experiment. Of course, in my trial experiment I’m going to change the thickness, length, and type of the material, in order to choose the best type of the material, thickness, and optimal range of lengths for my real experiment. In order to keep my experiment as accurate as possible, I’m also going to use a battery as a power supply instead of connecting the equipment into the plug and using normal electricity. I think that plugging the equipment in and using normal electricity is not very accurate, because some electric faults might happen, causing the decrease, increase or even a cut in the electricity. As a result this might affect the results in my experiment. Therefore, I’m going to use a battery as a power supply. While I’m setting up the circuit, I’m going to switch the power off. I’m also going to make sure there will be no risk for me and the other students, by using the crocodile clips very accurately and making sure, that while using, the wire doesn’t attract with the other subjects and materials. When I find out the optimal length of the wire, I will cut the wire. For example, if the optimal length of the wire is 55cm, I will cut 60 cm, in order to make sure I put the crocodile clips exactly at two points, 0 and 55. In my experiment I’m going to work in pair with another student. So, while he is taking the records, I will be measuring holding the wire straight, so it doesn’t attract with anything else. While taking the records, we are also going to be accurate, by using 0.00 measuring scheme, rather than 0.0, which is not as accurate as the first one. I will be measuring the results using a voltmeter and ammeter. There’s a reason why I think the voltmeter should also be used. The voltage supplied by the power pack cannot be regarded as a very accurate one. Therefore, I’m going to use voltmeter. Using of a voltmeter and ammeter will help me to measure the resistance accurately. After my partner and I finish taking the readings, I’m going to put them in the results table. In order to get accurate results, I’m going to repeat the real experiment twice. Then, after I’ve done this, I’m going to find an average amount of resistance for each length by calculating the average resistance of the results I will get, taking into the account both experiments (both repeats of the experiment). After I’ve done this, I will be plotting two prediction graphs, which will give me an idea of what the real experiment and graph will look like. According to these results I’m going to plot a graph. A real graph will go into the analysing and evaluating section.

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 shows 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

Поиск по сайту: