To find out the difference of resistance through a length of constantan wire.

Through my research of Ohm’s Law I have found how to calculate resistance, current and voltage

V=IxR

R=V/I

I=V/R

Prediction:

From my Research I have predicted that the longer the wire the more the resistance. We use 39AWG constantan wire. However if the wire is thicker the less resistance there will be as the free electrons will have more space.

Apparatus:

• Goggles   (see Safety)
• Constantan wire
• Power Pack
• Voltmeter
• Ammeter
• Wires (plastic coated)
• Crocodile clips (for plastic coated wire ends)
• Meter Ruler

Circuit Diagram:

Preliminary Experiment

The preliminary experiment makes sure I know how to set up the experiment safely and also get used to some Safety Rules ( see Safety)

The variable will be the length of wire we use.

The overall outcome will be the resistance

We must keep the type of wire and Voltage the SAME.

Method:

• Set up equipment (as shown on page 2)
• Activate power pack at a constant 4 volts.
• Take the readings from both voltmeters.
• Turn off power pack.
• Repeat this 3 times for every measurement used.( 10,20,30,40,50,60,70,80,90 and 100cm)
• KEEP THE VOLTAGE THE SAME TO ENSURE FAIR RESULTS.
• Calculate averages and therefore resistance using Ohm’s Law.

Safety:

• Girls and/or boys must tie up long hair.
• Goggles must be worn at all times.
• Tuck ties into shirts
• Make sure bags are not in the walkways.
• Put all stools/chairs under tables.
• Check that no liquid is near the experiment at any time.

Graph:

Original Results Table:

Analysis:

My prediction was correct because both graph and results table show that the resistance increased as the length of wire increased. From the graph I cannot see any immediate anomalies but anomalies can be caused by:

• Faulty connection to Voltmeter 1/2/ammeter/powerpack.
• Faulty equipment (e.g. wrong display on voltmeter 1/2/ammeter.)
• Incorrect measurements of wire length.

Evaluation:

Generally the experiment was a complete success, we were able to implement all safety precautions and complete the experiment in a controlled environment.

I could have improved the accuracy of the experiment in several ways:

1. I could have repeated the experiment so I had 5 tests per length which would give us a broader range and maybe a different resistance.
2. I also could have made sure there were no anomalies by buying new equipment just for this experiment, and -at a cost – improved the accuracy of my experiment.
3. To make sure our results were correct we could have cut precision (to the mm) measurements of constantan wire so our results were as pinpointed as possible.

We also could investigate several things further during our experiment that we chose not to do:

1. For example we could have used the cross section as a variable instead of/along with length.
2. We also could have used different metals with different chemical makeup, for example NiChrome wire made up of Ni, Co, Fe which would have different conduction properties to the wire we used and therefore would create a different set of results.
3. Knowing that heat affects the atoms in the wire which in turn affects the flow of current (free electrons), we could have increased or decreased the temperature which would deviate* our results.

In conclusion we found that many things affect the resistance in a length of wire mainly cross section diameter, wire length and wire temperature. If I was to do this experiment again I would definitely investigate further to give a broader range of results.

Physics GCSE Coursework 2005.