Planning Experimental Procedures

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Planning Experimental Procedures

Introduction

In this experiment I will make a circuit using different materials of wires. To alter the length of the wire to be tested I will use crocodile clips. Voltage will be measured by using a voltmeter. Amps will be measured using an ammeter. Then the resistance is to be calculated.

Key Factors Identified

One variable should be carried out at a time, to make it a fair test.

I am going to investigate what factors affect the resistance of a wire. Here are the main factors, which affect the resistance of a wire and some reasons as to why they affect the resistance of a wire:

The material of the wire (What the wire is made out of)

The length of the wire

The thickness of the wire (The diameter of the wire)

Temperature of wires

Contact resistance

The material of the wire

The material of the wire is important because different metals have different properties. Metals, as wires are different because copper is very good at conducting electricity, if you had very large lengths of copper wire then you would be able to see the resistance change. Electrons find it easier to pass through some materials then others. I am going to use nichrome, copper, manganin and Constantan.

The material of the wire when cut should be clearly labelled to prevent it from being mistaken as another material.

The length of the wire

The length will make a difference because when you have a long wire the electrons have to squeeze together to be able to pass through the wire than they do to be able to pass through a short wire. The longer the wire the longer the current has to travel so each electron is more likely to collide with the other electrons, slowing them down, causing heat to be produced.

When cutting the wire, use a ruler and be as accurate as possible.

The diameter of the wire

The diameter is a variable because the wider the wire, the more electrons can pass through. More on the diameter of wire will be explained in the scientific theory.

The thicker the wire, the easier it is for the ions to pass through it. If it is too thick then there won't be enough resistance to take recordings of.

I will be using 24 SWG, which is 0.55 mm in diameter.

Temperature

The higher the temperature, the higher the resistance because heat speeds up conduction and therefore increases the rate of electrons flowing through the wire.

We cannot change the temperature so we will leave it at room temperature, which is 24?c.

Contact Resistance

Contact resistance is important. The resistance is also dependant on how much the components and wires etc. are making contact. Also the material of the crocodile clips is a variable. I assume the crocodile clips are made out of steel. Steel has a low resistivity rate.

Fair Test Described

To make my experiment as fair as possible I will change one variable at a time. For example I can not have one experiment using 5 cm of manganin 24 SWG at 0?c, and another experiment using 5 cm of manganin 34 SWG at room temperature (24?c). The data from this experiment is useless to me because although the material of wire and length is the same, the SWG and temperature is different. I will change one variable at a time. For example I will use 5 cm of manganin 24 SWG at room temperature, 10 cm of manganin 24 SWG at room temperature and 15 cm of manganin 24 SWG at room temperature. This is will be a fair test because I will be changing one variable at a time. And also changing one variable at a time will help me compare my data instead of having 2 variables different. I am going to control each of the variables. I will control variable one which is the material of wire by carefully reading the labels on the wires when choosing them so that I am picking up the wire which I am supposed to. I will control variable 2, which is the length of the wire by cutting it accurately. I will use a ruler and as I cut the wire I will cut it at 90 degrees so that each of the wires have the same diameter. I will control variable 3, which is the diameter of the wire by cutting the wire at 90 degrees as I have just mentioned for variable 2. I will control variable 4 by using a thermometer to keep the room temperature constant. As I carry out my experiment the wires will get hot and this will effect the results. A way of preventing this would be to do this experiment in a fridge. If I drilled a whole either side of the fridge and had my tested wire through there hooked up to the rest of the circuit then the temperature would be constant because when the wire did begin to heat up. The heat would then be immediately lost to the environment because the fridge is cool.

There is not much that I can do about variable 5 because it is about the contact of each of the components in the circuit. I cannot measure how much the components are in contact with each other because I have no device to do so.

Scientific Knowledge

I am going to investigate which materials of wire have the highest resistance and I will combine it with the investigation about which lengths puts up the greatest resistance.

Resistance is a property that restricts the flow of electric current through it. Current is a flow of electrical charged particles that goes around a conducting circuit, this is caused by the potential difference. The current at any point in a circuit is the amount of charge flowing per second. It is measured in amperes using A or Amps as its symbol. It carries electrical energy from a power supply, this could be a battery of a power pack to the components of the circuit, where it is converted into other forms of energy, heat light or motion. Resistance is measured in ohms using the Greek letter omega. In this experiment I will incorporate Ohms Law in my calculations. This law states the current flowing in a metallic conduction maintained at a constant temperature, directly proportional to the potential difference (voltage) between its ends.

I will be using Nichrome 24 SWG wire. Nichrome (Ni) is made up of nickel and chromium, and other materials include iron, magnesium, silicon and carbon but in small amounts. Nichrome has a high melting point and is resistant to corrosion.

Copper (Cu) is one of the most widely used metals. It is a transition metal and has a high melting point

Manganin contains manganese, copper and nickel. It is mainly used in the form of wire for accurate electrical measurements because its electrical conductivity does not vary appreciably with temperature.

24 SWG is equal to 0.55 mm in diameter.

From doing my research into resistance of wire I have found that...

As the length increases

the resistance increases.

The graph on the left shows us this.

As the diameter increases

the resistance decreases.

The graph on the left shows us this.

The diagram on the right is a water

circuit; the pump is pumping water

around the circuit. As the water

passes through the wide pipe (Y) it

flows quicker than it does through

narrow pipe (X). This is because

water can flow through wider pipes.

Electrons pass around any circuit from the negative terminal to the power pack or battery to the positive terminal.

The rate at which the water is flowing is the current in an circuit how fast are the electrons moving. Resistance is what restricts the movement of the charge through the wire. The length of a pipe and its the cross-section, all prevent the flow of the water, and are associated to how electric current is impaired as it flows through a wire. Things like making the wire longer and thinner make the resistance go up since it is harder to push charge through the wire. Sometimes, some materials can be cooled down to very temperatures where they have effectively zero resistance, but in everyday encounters, effect doesn't really have much bearing.
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The reason for resistance in wire is because of the composition of the atoms such as copper, aluminium, of which a particular wire is made of and the arrangement of the atoms of these metals. When an electron passes through the wire, the electrons hit these atoms while making the journey from one end to the other giving opposition or resistance to the electrons.

When volt electrons move along the wires they hit atoms which creates heat through friction of the electrons and atoms.

Free electrons are attracted towards positive protons in the nucleus. ...

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