This is because in a piece of wire there are free electrons in the outer shell. These then become charged when a potential difference is passed across them. These electrons then arrange themselves in a line, and all start to move in the same direction, forming an electrical current. The electrons are moving but the other atoms are in fixed positions. As the charged electrons start to move, they collide with the fixed atoms. As they collide the electrons slow down and the current becomes less efficient, this is called resistance.
So the more collisions there are the higher the resistance will be.
So therefore the longer the piece of wire is, the more charged electrons and atoms there are, so therefore there will be more collisions, resulting in a increase in resistance. Also in longer piece of wire the electrons have to travel further and will collide with more atoms on their journey around the circuit.
For example; if there were ten collisions every 5cm’s of wire, then a piece of wire
50 cm’s long would have one hundred collisions. I m trying to explain that the longer the wire the more collisions it will have and therefore resulting in a higher resistance.
Prediction Diagram:
I predict that this is what is going to be happening inside the wire:
Apparatus:
Variables:
Independent:
- I will change the length of wire deliberately so I can see how a length of a piece of wire can affect its resistance. I intend to have the length of wire at 10 cm intervals,
(e.g. 10, 20, 30.)
Dependant:
The size of this variable, will depend on the independent variable:
- The current and voltage will be shown on the ammeter and voltmeter and I will record these. These readings will change as the length of the wire lengthens, which will enable me to find the resistance.
Controlled:
- The length of other wire, e.g. plastic coated will not change, because this wire is not being tested and may affect my results if changed.
- The temperature: if the temperature of the nichrome wire changes then this may affect my results. So I intend to only have the power pack on for 25 seconds at a time and then let to cool for 2 minutes. That may the wire wont over heat and give inaccurate results.
- I intend to keep the thickness of the wire the same, because I am investigating the length of the wire not its thickness.
- I will use the same amount of voltmeters and ammeters in the circuit because that may affect the resistance.
- I am going to use the same piece of wire throughout the experiment. Because different pieces of wire may have different properties.
Fair test:
The following points must be kept to obtain accurate and fair results:
- The room temperature must be kept constant, because is the temperature increases it causes the particles in the wire to vibrate rapidly and there will be more collisions and a higher resistance.
- The same wire must be used, because different wires have different properties and may have a different resistance.
- In each experiment the circuit set up must be the same, to be able to collect accurate results.
- All measurements must be measured to 2 decimal points. Because the experiment is being carried out with low quality equipment, which only measures to 2 d.p.
- The wire must be left to cool after the experiment, because from my preliminary work and my knowledge, the heat of the wire will affect my results. I know when the wire has cooled because the ammeter reading will stop changing.
- The experiment should be repeated two to three times in order to collect accurate results.
Safety:
The following safety aspects must be carried out whilst doing the experiment to enable the safety of the pupil, other people and their surroundings:
- When there are large currents going through small sections of a wire, there are could be large overheating. So it must be made sure that no one touches the wire during and up too 2 minutes after the current has run through it. The wire will go orange and smoke will be given off this can burn the table and can cause injury. This danger can be limited by not sending a large amount of current through the circuit.
- The wire can also give off an electric shock. So I must make sure that no one touches the wire because they will get electrocuted. To prevent this the power pack must be un-plugged, when the crocodile clips and the circuit is being re-configured.
- Keep your circuit away from water sources and taps, because water is a good conductor of electricity. Also never handle the equipment or touch the power supply while having wet handle, encase of an electric shock.
- Do not lay or obstruct the wire with other equipment or objects. Because the wire can get extremely hot and could cause things to melt or catch fire.
- Always ask a qualified member of staff to check your experiment before turning on the power, to check that it is set up safely and properly.
- A mat should be placed underneath the wire to stop the wire burning the table or work surface. Also, if the wire comes in contact with something else, it may affect my results.
Errors:
There are some things that I cannot stop to make it a fair test, but I can try and limit these as best I can. These errors may occur:
- I may get errors in my results if the wire becomes overheated from too much current running through it, and will therefore affect my graph.
- It is quite easy for me to make a wrong measurement, and make the wire too short or too long. It may only be 1mm either way but, that will still affect my overall results. So, I will measure the wire precisely from the inside edge of the crocodile clips, making sure the wire is straight when measuring.
- Errors may occur through broken or damaged wires. These may increase the resistance and affect my results.
- I must also make sure that the wire is straight during the experiment, because if not, short circuits may occur. I must also straighten out any bends because this could cause extra-unwanted resistance.
- Since my experiment is spread over 2 weeks, the room temperature between those two weeks may differ. This may slightly affect the heat of the wire and my results. Therefore I would not have carried out a fair test, and my results, would not be accurate enough to support a firm conclusion.
Range Measurements:
The lengths of the wire will be 10, 20, 30, 40, 50, 60, 70cm across three different power pack readings 4, 6, 9 p.d. I decided to use these measurements because they were systematic, and from my preliminary work I can tell that these measurements of the independent variable will give me an accurate range of results, whereby I can write a firm conclusion.
Diagram:
Circuit:
Wood and Wire:
On the wood, measure out 10cm intervals up to and including 70cm. This is too let you know where to connect the crocodile clips. The nichrome wire should never get cut or become unattached from the wood.
Method:
- Set up the equipment as shown in the two diagrams.
- Make sure the voltmeter is connected in parallel to the wire. Now spread the crocodile clips so they are 10cm apart on the wire.
- Turn the power pack on to 4 p.d and record the ammeter reading in amps and the voltmeter in volts.
- Only have the power pack on for a maximum of 30 seconds or the wire becomes too hot. Once the power pack has been turned off, wait 2 minutes before turning back on.
- Now move the crocodile clips 20cm apart along the wire and repeat as before. Now repeat at 30, 40, 50, 60, 70cm at 4 p.d and then repeat the whole experiment at 6 p.d. and 8 p.d.
- Pack all of the equipment away; do not move the wire until it has completely cooled. Turn of the power pack at the mains, before disconnecting the circuit equipment.
Find the resistance of the wire in ohms ( Ω ). Refer back to Preliminary Knowledge
Results:
The current and Voltage of the wire at different lengths:
Resistance of the wire at different Power Pack Readings:
Average Resistance for the power pack readings:
Conclusion:
From my results and graph I can clearly see one very clear a pattern forming between the length of the wire and the resistance of it. I can say that the length of the wire is directionally proportional to its resistance. That is, as the piece of wire increases in length, the resistance of the wire also increases. Another significant aspect of the experiment is that this increase is constant, throughout the results.
Different power pack readings (p.d) had no affect on the resistance at all.
From the graph I can see a very clear pattern forming. The length is directly proportional to the resistance on every point on the graph. It clearly shows that as the length of wire increases, so does the resistance. There is a positive correlation, and another significant thing is that; the increase remains constant. I also found the gradient of the line and that remains constant throughout the line graph.
My predictions were very accurate; these were based on my preliminary work. I was predicted that as the length of wire increases and the resistance would also increase. I was completely right, my graph prediction was also very accurate.
As the power pack reading (p.d) increased, so did the electric current. I know that current is the flow of electrons in a circuit. In the short lengths of wire (i.e. 10cm and 20cm) the current was high. This tells us that there was a good strong flow of electrons with very few collisions with atoms, and they were working at a efficient rate. I can verify this because the short lengths of wire had a very low resistance. As the power pack was turned up the current increased and the electrons were moving faster and had few collisions. But as the length of the wire increased the current decreased. This tells us that electrons were colliding a lot more with the other atoms. When the electrons collided they slowed down and this caused the current to decrease. So as the current decreased and the electrons kept colliding in the longer pieces of wire, the resistance was increasing.
The wire’s resistance increases as the length of the wire increases due to Electrons and Atoms colliding more often. The free electrons in the wire became charged when the potential difference was passed across them, from the power pack.. The electrons then arrange themselves in a line, and all started to move in the same direction (electric current). As they started to move they started to collide with other atoms, which were in fixed positions. As the electrons collided they slowed down and the current decreased, this is called resistance.
In the shorter lengths of wire, there were few electrons or atoms, which meant very few collisions. That why from my results I can see that the current was high and resistance was low. But as the length of wire increased there were more atoms and electrons, which meant more collisions, which resulted in a lower current and higher resistance. Also the electrons had to travel further, if the wire was longer, which meant more collisions on its journey.
A diagram of the 10cm Wire:
(This is an estimate of figures, just to prove my theory)
In the 10cm wire there were very few atoms or electrons, and therefore were very few collisions, and the resistance was low and the current was high.
A diagram of 70cm Wire
(This is an estimate of figures, just to prove my theory)
In the 70cm wire there were lots of atoms and electrons, and therefore there were a lot of collisions, resulting in the resistance was high and the current was low.
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