The Factors that affect resistance.

GCSE Science

The Factors that affect resistance

Four main factors affect resistance in an electrical circuit

Length
Cross sectional area
Temperature
Material of wire

How I will stop the Variables from varying

Cross sectional area - The same piece of wire was used in all parts of the experiment. It was gently attached to the ruler so that there was no movement and no strain put on the wire which might change the cross sectional area.

Length – This was achieved by measuring the wire so that the variable was only changed on purpose.

Temperature – I will control it by only running the electricity through shortly to minimize the heating effect and with cooling time in between.

Material of wire – The same piece of wire will be used so there is no variation in the type of material use.

In my investigation I will only be changing one factor each time to keep my experiment fair. In the experiment I will only be altering the length of wire I use every time.

In my experiment I am using this apparatus

Wires
Crocodile clips
Power supply and cable
Ammeter
Volt meter
Meter ruler
The piece of wire that I am testing (0.2 width)
Sticky tape

I predict that the longer the wire the more resistance there will be in the piece of the wire because as the current passes along the wire it has collisions with other electrons causing waste energy and resistance. . Ohm’s law says that by taking the ratio of volts to ammeters the resistance of a piece of wire could be calculated. An electrical current is a flow of charged particles from an area of high potential to an area of lower potential. For my background information I used the GCSE Double Award Physics textbook written by K Foulds and Asimov’s Guide to Science written by Dr Isaac Asimov.

I will assemble the equipment as the diagram at the top of the page shows. The power supply was plugged in to the wall and the setting was switched to a variable current. The 0.2mm wire was selo-taped to the meter rule and the Crocodile clips placed at the beginning and the end of it. These Crocodile clips were attached to an Ammeter and the power supply. Another set of Crocodile clips were attached to the wire at the specified lengths and these were then attached to a voltmeter.

The current is measured using the Crocodile clips attached ...

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The current is measured using the Crocodile clips attached to the Voltmeter at the length that is being measured. The measurements go up in 10-centimeter intervals 10-50 cm. For each measurement it is repeated 3 times on each of the different volts 1v, 1.5v, 2v. The readings will be taken for the different lengths at 3 different currents 1V, 1.5V, 2.V the whole process will then be repeated another two times so that enough results can be collected in case of an anomalous reading.

To make my test fair

I will only change one factor the length of wire I am using each time.
Ohm’s law will only help if the temperature is kept the same.
The power supply must be turned off after each reading to keep the apparatus cool.
The wire will cool every time the power supply is turned off.

To ensure the safety

Keep all water away from the experiment.
Do not touch the hot wire.
The power supply will not be continuously left on.
Do not leave the experiment going unattended.

To make sure that I have chosen sensible lengths and voltages I am doing a preliminary experiment. The test will be set up in the same way as the real experiment, which has been shown in the diagram. I will test the two extreme lengths and volt measurements, so I can see if the experiment will work at the two extremes.

In my preliminary experiment I attached the Crocodile clips that were connected to the power supply at either end of the piece of wire. This was not a good idea because there is a lot of resistance in the wire. So instead I have attached the Crocodile clips to the wire 70cm apart. This is far enough for me to collect all the results I need at the different lengths and for my experiment to reach all the required volt readings. The preliminary proved that the 10cm intervals were of a suitable distance for the results of this experiment.

My results show that as the length of the wire increases so does the amount of resistance. This proves my prediction in which I said that the amount of resistance would increase as the wire got longer because there would be a larger surface area with which collisions could occur leading to a higher level of resistance. The line on my graph shows that as the length of the wire increases so does the average rate of resistance. In my table of results this can also be seen as the results increase as the wire gets longer. Doing the experiment 3 times has made sure that I have not recorded anomalous results, which would make my theory harder to prove.

My results were accurate and helped me to prove my hypothesis, none of the results I collected were anomalous. The results were reliable for proving my prediction but they were not 100% accurate because they can only be as accurate as the equipment records the result e.g. to one decimal place.

Sources of error

Paralex error could have occurred on all of the readings and the measurements.
The length of the wire was only accurate to 1mm.
The Volt and Ammeter readings were only accurate to the precision of the apparatus.

Preventing errors

The paralex error could be minimized by standing in the same place with the same angle of vision the apparatus.
The wire could not be measured more accurately due to the fact that there were not more precise rulers.
More precise Volt and Ammeters could be used or digital ones.

To take this experiment further I could see if the rate of resistance is affected I use different types of metal wire. I could use wires made of different materials and see if the materials also influenced the resistance as well as the length of wire.

Another way of extending this experiment would be to use wire with different cross sectional areas and see if this would affect the resistance.