Aim: To investigate if the length of wire affects its resistance.
I predict that the longer the wire the higher the resistance, and the shorter the wire the lower the resistance.
Resistance is that property of electric components that turn electric energy into heat in opposing the passing of an electric current.It can be beneficial, as in electric heaters, or a pest, as in light bulbs, where the heat is produced alongside the light – we want maximum light and minimum heat. Reistance is often unwanted and we try to minimise it since it results in lost energy, which costs money. Lately superconducters have bee in the news a lot. The are very special conductors which have zero resistance when cooled to a very low temperature. Current may flow for months or years with no measurable loss even when the applied voltage which started the current flowing is removed. There are two equations which determine the amount of current and the power converted into heat in a resistor: V=IR and P=VI respectively, where V is the voltage in Volts
I is the current in Amps
P is the power in Watts
R is the resistance in Ohms
The reciprocal of the resistance, 1/R, is called the conductance and is expressed in units of reciprocal ohm, called mho. Some of the properties of resistance may be summarized in a series of bullet points.
• If you use resistances in series circuits you get a higher resistance. • If you use resistance in a parallel circuit you get a lower resistance. • If you use different materials you receive a different resistance. This may because of the internal structure of the material, the way the atoms Aare arranged, or the type of atoms of which the material is made. • When metals are heated their resistance goes up.
• When semi-conductors are heated their resistance goes down.
These are the factors we are going to control: keeping these the same for each test will ensure our results are as fair and accurate as possible.
1. Ensure the temperature is always the same, by doing the experiment in a thermostatically controlled room 2. Ensure you always use the same equipment for this may tamper with results. 3. Ensue you use the same type of wire (for reasons explained in Knowledge) 4. To redo tests several times and create an average to stop outliers. 5. Keep the Voltage the same for each measurement.
6. Keep the thickness the same.
• Metre Ruler
• Power Supply
• 1 metre length of wire
• Wires for power supply and ammeter.
Ensure no live high voltage wires are exposed; this is done by having a small voltage of 2V. Wear safety goggles to protect eyes from the power supply. Work in pairs to prevent any dangerous incidents occurring. Make sure that all taps are turned off to prevent possible electrocution. Be quiet, talk sensibly, do not shout and always listen to your teacher.
Method and Diagram:
Step 1: I put on my safety goggles.
Step 2: I set up my apparatus.
Step 3: I switched on power supply to 2V.
Step 4: Fixed wires to power supply and metre ruler with the wire. Step 5: Attach second wire to the ammeter.
Step 6: Leave a ‘loose’ wire from the ammeter so that you can record your results. Step 7: Move the ‘loose wire along the metre stick with the wire at different lengths (20cm, 40cm, 60cm, 80cm, and 1m) and record results from the ammeter. Step 8: Repeat Step 7 three times and create an average.
Step 9: Divide the voltage (2V) by the average results (in Step 8) to find the resistance.
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