 # The Effect of the Length of a Nichrome Wire on Its Resistance Background Information: What is Current and Voltage? Atoms consist of three particles (protons- positively charged, electrons-negatively charged and neurons- neutral). These particles are the process to how electricity travels round a circuit. The flow of electrons around a circuit is current. Current works through a circuit as the negative terminal of a battery repels the negative electrons forcing them along the wire and the positive terminal of a battery attracts the negative electrons along the wire. Current is measured in amps- this measures the rate at which the electrons are flowing through a circuit. 1 amp would be 6 million million million electrons flowing around the circuit. Current is the same at all points round a circuit. Voltage is the force that moves the electrons around a circuit. The higher the voltage the more push force given to the current.
Voltage is measured in volts- this measures the push force. Moving round a circuit from one terminal to another of the voltage across the components is equal to the voltage across the battery. What is Resistance? Resistance is Ohm?s Law Ohm?s Law states: ?the amount of current flowing through a wire is proportional to the voltage?. The formula is stated below: V= I x R R= resistance V= voltage I= current Factors that affect resistance of a wire: Temperature: the temperature affects the resistance of a wire because when the temperature increases the resistance increase as well. The reason for this is when one or more of the outer shells are lost from the metal atoms the metal atoms turn into positively charged ions. There are also free electrons (current) surrounding the positively charged ions this can also be described as a sea of negatively charged electrons moving through a fixed arrangement of positively charged ions. Since there is a force (voltage) pushing the electrons round the circuit the electrons collide with an ion. The ion vibrates at its fixed position as the electron has transferred its kinetic energy to the ion? The more electrons collide with an ion the hotter the wire becomes. Since there are more collisions, there is less current going through the circuit, increasing the resistance therefore increasing the temperature. As for this experiment, we do not want to vary the temperature so the temperature will be kept constant. Length: doubling the length of a wire double it resistance. This is because with a short wire there is a smaller distance therefore the electrons can collide less often as there are fewer ions so this decreases the resistance, as there is more flow of current. However, with a long piece of wire there is an increased distance therefore the electrons collide a lot more as there are an increased number of ions as a result this increases the resistance. Cross Sectional Area: resistance decreases if the cross sectional area is increased. The reason being is that thinner wires have more resistance as the space is narrow the electrons have less freedom to move so they collide more often. However, the thicker wire has less resistance Material: insulators have a higher resistance than conductors as conductors have more free electrons meaning that they have a stronger current than insulators since insulators resist electrical current giving them a high resistance. Nichrome has a higher resistance to copper as Nichrome is made out of nickel and chromium which makes it impure this means that there are more ions this leads the electrons to easily collide with the ions while copper is a pure metal the electrons can easily pass through as there are less ions to collide with. Nichrome is a good insulator and copper is a good conductor. Prediction: I predict that the longer the nichrome wire the higher its resistivity. This is because Nichrome is an impure metal as it made from nickel and chromium meaning there will be more electrons colliding with the ions this in turn produces a high resistance. In addition, as the electrons have a further distance to travel they will collide with more ions than in a small lengthen wire. Therefore, if you increase the length of the wire there will be more nickel and chromium ions for the electrons to collide with. Below is a prediction of how the graph should turn out: [image] C [image] U R R E N T (A) [image] voltage (V) Metal wire usually obeys Ohm?s law. Accordingly, the Nichrome wire should give a graph that the current is directly proportional to the voltage (a straight line which goes through the origin) this shows that the nichrome wire is obeying Ohm?s law as Ohm?s law states: the amount of current flowing through a wire is proportional to the voltage, at a constant temperature. Therefore, this would make the Nichrome wire an Ohmic resistor. To work out the current, voltage and resistance I use Ohms law?s formulas: I= V/RV= irr= I/VI= current V= voltage R= resistance These formulas will help me to understand the relationship between the resistance of the nichrome wire and its length. Apparatus:
5m of nichrome wire, for the charge to travel through.
Crocodile clips, to connect the circuit.
Wire cutter, to cut the wire down to the desired length
Metre stick, to measure the different lengths of wire.
Connecting wires, to carry the electric charge.
Voltmeter, to record volts.
Ammeter, to record amps.
Method:
Set up equipment as shown in diagram above.
Cut a 20, 24, 28, 32, and 36swg nichrome wire to 100cm using a
metre stick.
Start at 20swg and add it to the circuit.
Start at 100cm record the results and move the crocodile clip down
10cm.
Record the results from the ammeter and the voltmeter onto a
table.
Move the crocodile clip down 10 more cm and so on until you get to
the end.
Change wire to the next gauge and gradually work your way through
all of them.
Repeat the 24swg three times at all lengths.
For all the thicknesses record the results three times at 50cm.
Then find the resistance using the equation R=V/A
Plot the graphs.
Safety
Make sure bags and coats are in a safe place where nobody can fall
over them
Walk in an appropriate manner around the laboratory.
Leave the wires to cool before touching them
Do not take water near the power pack and don?t have the voltage
too high
Fair Test I will make this experiment a fair test by using the same type of wire i.e. not changing the diameter or changing it to a copper wire instead of nichrome. I will record the results three times, reducing errors. I will let the wire cool down before going onto starting on the next length as the current cause?s heat I will need to let the current go down. I will use the same amount of power that means there is the same amount of electrons in passing along each wire. I will check the circuit is connected together properly each time. The experiment will take place at room temperature and it will be kept constant, as this will prevent it from interfering with the current. Results Table: Length Voltage (V) Average Current (A) Average Resistance (ohms) To 2 d.p 1 2 3 1 2 3 1 0.2 2 0.4 3 0.6 4 0.8 5 1.0 Calculations: Average: Add up the 3 voltages and the three currents then divide by 3 Resistance: Average Voltage/ Average Current I carried out a preliminary experiment to make sure the lengths were appropriate for the investigation. Instead of going up in 50 pattern I decided for a 20 pattern as in the 20 pattern you can fit five lengths but with 50 only two. With a 20 pattern, it would cover the whole variety of lengths (long, medium, and short). In addition, it would give a good set of results that would advantage me when I am drawing the graph.

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