A.S. Physics Practical Coursework Resistance of Nichrome Wire

SAFETY

I will have to consider this as I am experimenting with electricity, so:

Although it is obvious I will also have to be careful when cutting the nichrome wire, making sure I don't get the pliers ends onto my fingers!

I will make sure that I do not conduct the experiment near the sinks in the laboratory. This is because I could electrocute myself if any water were to spill onto any part of the experiment.

When I am connecting the crocodile clips onto the wire I will ensure that the power supply is turned off from the mains. I will turn off the power supply when I am taking off the clips.

I will make sure that the wires are not crossing over each other.

The crocodile clips must not touch each other whilst the power supply is on as it will cause a spark.

I will try to set-up my experiment away from other students as our experiments could cross over; the clips might touch each other causing a spark (basically to ensure the experiment is safe from students).

Make sure that experiment area is clear of any objects apart from the necessary apparatus especially any other metals (good conductor of electricity).

No loose connections.

APPARATUS:

* Power Supply {Will be set at a constant of 0.5 Volts}.

* Nichrome wire {Different thicknesses & lengths}.

* Leads {To connect to the power supply, which is connected to crocodile clips}.

* 1 Metre ruler {Get lengths from 10-100cm}

* Voltmeter {Measure voltage from two points, 2V}{Digital Multimeter}

* Ammeter {Measure current between two points, 200mA}{Digital Multimeter}

* Masking Tape {To hold down metal wire}

METHOD:

* First I will collect all my apparatus.

* I will connect the leads with the power supply, clips, voltmeter & ammeter.

* Also, I need to ensure that none of the connections are loose; this is to ensure safety.

* After, the connection checks have been carried out; I will begin to set-up the experiment. While proceeding with the set-up I will have to make certain that the leads do not cross each other. Therefore, the leads will be placed neatly.

* Cut slightly over desired length of wire.

* Place it on top of ruler and secure it by placing masking tape over the wire and ruler. Tape should be stuck on away from the desired points where the clips will be.

* Place clips at two points from the greatest distance and decrease length after each experiment i.e.: 100cm, then 90cm....10cm.

* Calibrate power supply to 0.5 Volts. Then activate the power supply after the clips have been placed on the points.

* Measure the voltage and current at each length.

* Deactivate power supply after each reading.

* Record readings and calculate resistance using R = V/I plot graph.

* Plot resistance against 1/A to show that R?1/A. 1/A means 1 divided by the thickness for e.g.: 0.19mm.

* Plot Current against thickness to prove that as thickness of wire increases so does current.

PREDICTIONS:

Predictions as follows:

* As far as finding a relationship between resistance and length the data when put onto a graph should be a straight-line graph (must start from 0,0 origin). This is because it is a well-known fact that R?L. Electric current is the movement of electrons through a conductor. In this experiment a metal wire (Nichrome will be the conductor). So when resistance is high, conductivity is low. Metals such as Nichrome conduct electricity well because the atoms in them do not hold on to their electrons very well. Free electrons are created, which carry a negative charge, to jump along the lines of atoms in a wire, which are in a lattice structure. Resistance is when these electrons, which flow towards the positive, collide with other atoms; they transfer some of their kinetic energy. This transfer on collision is what causes resistance. So, if we double the length of a wire, the number of atoms in the wire doubles. This increases the number of collisions and energy transferred twice, so twice the amount of energy is required. This means the resistance is doubled.

* To find the relationship between resistance and area I believe that the results will show that they're proportional. I say this because it is known that R?1/A. So the graph for these results should show a straight line as well.

* Also I am using a certain type of material, which has different properties from other materials one, which includes resistivity (?). The resistivity of a material will decide upon how well it allows the electrons to flow through. The resistivity can be found out at the end of the experiment using the following formulae:

? = RA

L

FACTORS AFFECTING EXPERIMENT:

When doing my experiment the things that will affect my results are time, reliability and availability of resources.

The time factor of this experiment is an obvious one. Though I do not believe it will affect my results too much. Reliability will affect my results slightly. Coming back to the time factor because of the limited time I may rush things, which may affect accuracy.

When I place the clips on the wire I may not place them exactly in there accurate positions give or take 0.2cm. This will affect the results slightly. The apparatus I will be using is frequently used so, there is a possibility that for e.g.: the ammeter may not read the value of the current accurately but it probably won't be by much.

I have thought of ways to tackle these problems as best as I can. The only factor I can't change is time. To make my results as accurate as possible I will make sure voltage from the power supply is constant, which I have decided will be 0.5V. So, that I have as accurate results as possible I will repeat results so, for e.g.: the placing of clips can be accounted for and

this way it shouldn't affect the results tremendously. To avoid damage to the part of the wire, which I will be placing the clips on I will cut the wire longer than necessary. I will check if the ammeter and voltmeter are as accurate as possible by putting through a certain voltage {from a power supply} and see on the LCD screen if it measures accurately.