To investigate the factors present in a wire (and the circuit that it is connected to) which affect the ability of current to flow through it.
HOW DO FACTORS PRESENT IN A WIRE AFFECT ITS CURRENT?
PHYSICS COURSEWORK- OCTOBER 01
BY LISA NIGHTINGALE
AIM- To investigate the factors present in a wire (and the circuit that it is connected to) which affect the ability of current to flow through it.
PREDICTION-
There are many factors present both in a wire and its circuit which would affect the current in the wire:
FACTOR
HOW DOES IT AFFECT THE CURRENT?
HOW CAN YOU CONTROL IT?
Thickness (diameter)
Allows more/less current to pass through the wire in a space of time. The thicker a wire, the more options there is for the current to flow easier, than with a thinner wire.
Using the equipment available, there is no means of controlling the wire's diameter this is because we have to use the same wire throughout the experiments, for the whole investigation.
Conductivity
And
Density
(material)
Allows easy/ hard passage through the wire. Different materials have different conductivities. This is dependent on their densities. The more dense a material is, the less well it will conduct electricity. This is because there is less room for electrons to move and current to continue flowing.
There is a choice of using two metals, ni-chrome, and constantan. These are both of different densities and the density of each remains constant during the experiment so it does not need to be controlled manually. The fact that we are using the same wire throughout the investigation and we are not switching between the two shows how we keep these two factors constant.
Length
The length of wire is a factor in the resistance and the heating effect of the wire. The longer the wire is, the more the resistance will increase. This is because the electrons find it harder to travel over longer distances, and effectively "tire". Therefore, the current will decrease as the length increases.
This can be controlled very easily by simply placing the crocodile clips which are attached to the rest of the circuit at different points along the experiment wire to include it in the circuit thus registering different lengths of experiment wire. The measurements will need to be very accurate, and all lengths will be measured to the nearest millimetre, rather than centimetre.
Heating effect
The heating effect affects the wire by deciding how quickly the wire will heat up. If it is quickly, this could cause the wire to snap or melt in one point. It also affects the resistance of the wire.
The heating effect can be controlled by not allowing the wire to heat up. The power pack can be turned on and off quickly when taking a reading from the ammeter (the voltmeter reading will remain constant.) The wire will also be allowed to cool between readings so that the heating effect does not take effect.
Voltage
The higher the voltage being outputted by the power pack, the higher the work rate will be. If the work rate is higher, then the flow of current will be increased.
The voltage can be controlled using the voltage being outputted by the power pack, and the variable resistor. To use the variable resistor effectively, to keep voltage constant, you must take the minimum and maximum voltage (found using the variable resistor) over the minimum and maximum length of wire being experimented on, and choose a constant voltage which occurs in the overlap of these ...
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Voltage
The higher the voltage being outputted by the power pack, the higher the work rate will be. If the work rate is higher, then the flow of current will be increased.
The voltage can be controlled using the voltage being outputted by the power pack, and the variable resistor. To use the variable resistor effectively, to keep voltage constant, you must take the minimum and maximum voltage (found using the variable resistor) over the minimum and maximum length of wire being experimented on, and choose a constant voltage which occurs in the overlap of these readings.
Current = Resistance x Voltage, so, the higher the voltage is, the higher the ammeter reading will be.
Resistance
The resistance controls how much the flow of current is opposed. If there is a high resistance, then it will be greatly opposed, if there is a low resistance then it will not be so opposed and the current will flow more easily.
The resistance of the wire will be changing as the length of the wire changes. This can be done by taking the minimum and maximum voltage (found using the variable resistor) over the minimum and maximum length of wire being experimented on, and choosing a constant voltage which occurs in the overlap of these readings.
I have chosen to investigate the length of the wire, to see how it affects the current flowing through a wire. I predict that the length will affect the flow of current in a negative way. I think that the longer a wire is, the harder it is for current to flow between two points on it. The obvious reason is that the current will take more time to travel between farther points whilst travelling at the same speed, although the difference would be minimal.
Ohm's law plays a key role in predicting how the length of the wire will affect the current in it. Another law to do with resistivity states that:
R = pL/A
Where R = Resistance (ohms)
p = the constant resistivity of the metal (ni-chrome) (ohms/metre)
L = length of wire (metres)
A = cross- sectional area of wire (squared metres)
The cross-sectional area and resistivity of the metal both remain constant, therefore resistance is directly proportional to the length of wire.
Ohm's law states that:
R = V/I
Where R = resistance (ohms)
V = voltage (volts)
I = current (amps)
The voltage is remaining constant in this experiment so R is directly proportional to 1/I. If R is also directly proportional to L then L must also be directly proportional to 1/I. If R and L are directly proportional then as one increases so does the other. I would therefore predict that as I increase the length of wire being experimented on, the resistance of the wire would increase.
Resistance is increasing and voltage is remaining constant, therefore the current must be decreasing. This decrease is caused by the increase in resistance. I can thus predict two graphs that would occur from this experiment:
The current-length graph looks like this because the current decreases as the length increases. The graph is of negative correlation, and levels out towards the end. The current should decrease at a fast pace in the beginning, and then decrease at a slower rate until it evens out. This is because the current can pass through a shorter wire quickly, but as the wire increases, the rate at which the current decreases is also increased. This is because the resistance increases (at a steady rate) but the voltage remains constant. The graph should curve because it is a 1/x graph.
The resistance- length graph should be a straight line of negative correlation. It will be straight because the resistance is directly proportional to the length of the wire, and will also pass through the origin. The resistance increases with the length, and also increases at the same rate throughout. The graph should not curve because it is a 1=x graph.
Another reason as to why the resistance should increase is because there are atoms present in wires. The longer the wire, the more atoms there are present in it. Therefore there are more obstacles in the wire for the electrons to be obstructed by. This will "slow" the electrons down, or offer increased resistance.
I can also use a model to show how the current would flow differently through different lengths of wire. I will use the model of people walking through a corridor. The corridor width remains constant. If a corridor were short, then people would be able to walk through it quickly. There would be no pushing from others, and it would be fairly simple. As the corridor increases in length, so does its capacity. It can hold more people; so more people enter it. It is more crowded so becomes harder to pass through. The same is true for electrons passing through a wire. They have a constant force pushing them from behind. This is the same as the constant speed that the people in the corridor are walking at. As a wire increases in length, so does its capacity, as with the corridor. This allows more electrons into the wire, making the wire more crowded. This in turn makes it harder for the electrons to pass through. There is increased resistance. The opposing force is all the people at the far end of the corridor that are blocking it for those trying to pass through/ enter. The other people or electrons are like obstacles that need passing. They are there to oppose the electrons. They are resistance. Therefore, the wire (or corridor) length increases, which increases its capacity, therefore increasing its resistivity which means that the flow of current, or the speed at which people pass through the corridor, will decrease as the length of the corridor/ wire increases.
FAIR TEST-
To ensure that this investigation is a fair test, I must control all other factors within the experiment apart from the one that I am investigating.
. I will measure the diameter of the wire using a micrometer screw- gauge. I will measure the diameter at three different points along the wire, so as to get an average diameter because as the wire is old, it is likely to be of a different diameter at various points. Therefore the fairest way to conduct the experiment and obtain results is by measuring an average wire diameter.
2. I will keep voltage constant within the circuit by placing the crocodile clips at the points on the wire which are my minimum experimenting distance (50mm) and reading the minimum and maximum voltage achieved through the circuit using the variable resistor. I will then repeat this for the points on the wire which are my maximum experimenting distance (500mm.) An overlap will occur between these two sets of voltages. The constant voltage to be used should be chosen from within this overlap and the variable resistor will be used to keep voltage constant throughout the experiment.
3. The same equipment should be used each time the experiment is performed to ensure that anomalies do not arise. Different power packs have varying outputs and the digital voltmeters and ammeters are not as reliable as they could be. If the same equipment is used throughout, then the equipment can be ruled out as the cause of any anomalies. The same wire must be used, as it is probably the only wire available that has the same density/ diameter etc.
4. I will keep the temperature of the wires in the circuit constant to prevent the whole circuit from overheating. I can to do this by quickly switching off the power pack every time I record a set of results. I can then leave the power pack to rest for a small period of time before switching it on again to record the next set of results.
5. I will make sure my experiment is accurate by measuring length in mm instead of cm. I am using a micrometer screw- gauge, which is very accurate at measuring small distances to measure the diameter of my wire.
SAFETY-
It is important to be safe whilst working in a lab in school, especially when working with electricity. I will be sure to:
* Not touch the wire after recording results, as it is likely to be hot, and I do not want to sustain any burns.
* Tie my hair back. Again it is a danger around the hot wire, or any loose connections where it could become burned or electrocuted.
* I will make sure that no equipment is faulty and that all connections are secure and not likely to become loose and cause danger of electrocution.
* I will also make sure that the power supplied is not too great, because if it is, then the wire could snap or melt, or even explode, which could be VERY dangerous.
* When working with electricity it is important not to be silly and fool around, because it could lead to accidents.
* I will make sure that all equipment is set up neat and tidily on the desk. This is to ensure that there are no loose wires or pieces of equipment strewn on the floor where somebody could trip over them.
* I must make sure that all belongings such as books and bags are also neatly away, also to prevent tripping, which could lead to other problems.
* I will tighten the wire to ensure that there are no kinks in it which would affect my measurements and probably my results.
APPARATUS-
* Power pack
* Ni-chrome wire, attached to a wooden block
* 2x crocodile clips
* Ammeter
* Voltmeter
* Variable resistor
* 6x wires
* Screw-gauge micrometer
* Ruler
DIAGRAM-
METHOD-
. Set up the apparatus as shown in the diagram above. Make sure that the voltmeter is connected in parallel to the circuit, and the ammeter in series.
2. Measure out 50mm intervals along the wooden block that the experiment wire is attached to until 500mm has been measured.
3. Measure all variables as stated in the prediction and fair test sections to ensure that they are constant. Follow the methods stated previously clearly to ensure that this is done accurately.
4. Set the voltage of the circuit at 0.40 .
5. Place one crocodile clip at the point marked "0" on the piece of wood. Place the other 50mm away. Take three readings from the ammeter, taking care to turn the power pack off and on again between each reading to prevent the wire from heating.
6. Repeat this 9 times, at each 50mm interval, continuing until three readings are taken at the 450mm mark.
7. Put the results into a table and work out the average current at each length (50-450mm) of wire.
8. Draw a graph of results.
RESULTS-
Type & Avg. diameter of wire
Length of wire (mm)
Voltage
Current 1
Current 2
Current 3
Avg.
Resistance
V/I
Resistance
pL/A
Lisa Nightingale 11aT
