Hows does changing the length of wire affect resistance?

Topics: Orders of magnitude, International System of Units, Electric current Pages: 6 (1394 words) Published: July 11, 2004
OBJECTIVE

For this piece of coursework I have been asked to investigate into the resistance of wires when the length is changed.

INTRODUCTION

The objective for my coursework (as already stated above) is to investigate how changing the length of wire can affect the resistance.

There are factors which can affect how accurate our expriment is come on four levels.

As in any scientific experiment, there are always variables ( "likely to change or vary subject to variation; changeable." ) which can alter a potentially good set of results into a bad set full of anomalies. In this particular test there are five main variables.

Length affects resistant, this is the variable which we are changing. As water in a hose pipe, the longer the pipe the longer the water takes to reach its destination. This can be applied in the variables of resistance. The electrons 'bounce' off the atoms - this causes the electrons to head elsewhere rather than the desired direction. In a long tube there are more atoms, this slows the electrons down as they 'bounce' off into another direction. In a short tube, there are less atoms which means there are less to deflect the electron any more speeding the speed up. In theory, the length should be proportional to the resistance. This is the variable which we will be changing in the experiment.

Diameter, we are keeping the same. Again, with the hose pipe, if the tube is thick it allows more water molecules to pass through at one time compared to a thinner tube. Once again this can be applied to resistance in wires.

If the wire is 'thin' then there are less paths for a electron to travel. This slows down the electron slowing down the speed. If the wire is thick then it allows more paths for the electron to follow and therefore, speeds up the flow of electrons.

Both Length and diameter work with each other. A thick wire that is long has more atoms but also more paths, these "cancel each other out" and may cause the electrons to move faster but have to move further. Vice versa with short thin wires. We keep this the same by not changing the wire throughout the whole experiment.

If the wire is heated, the atoms will move around more because there will be an increase in energy. This would cause more collisions between the atoms and the electrons. The increase in collisions would cause the resistance to rise. We keep this variable the same by turning the power of nearly straight after we have seen a result (without it fluctuating) too keep the temperature down.

The choice of materials that we could use for the wire affects the resistance that we receive. A wire with too little resistance would be hard and complex to collect results due to a 5th or 6th decimal point change. A wire with a lot of resistance may not let any current through at all making it hard to take down a result. We keep this variable the same by keeping the material the same.

METHOD

APPARATUS

Crocodile Clips

Power Supply (Power Pack)

Wires

Chrome Nickel

Ammeter

Voltmeter

Metal Ruler

4.5v bulb

METHOD STEPS

(BASIC OVERVIEW)

Decide which wire to use by creating a simple test of the most varied results

Measure 100cm of the wire and attach to a metre ruler.

Ÿ Check equipment works well;

Power source

Connecting wires

Ammeter

Voltmeter

Ÿ Set up the appropriate circuit

Ÿ decrease the length of wire by 10cms

Ÿ Write down Voltage and the current in the circuit

Continue until the two clips are touching at 0cms

Ÿ Repeat two more times to give more reliable results

METHOD

(ADVANCED)

At first we conduct tests on two sets of wire - copper and chrome nickel. This was so we could decide which was the most suitable wire to use, if we were to use a wire which had extremely low resistance the changes would too minute it would be impossible to take down results since both ammeter and voltmeter were only capable of showing to two decimal places. If we were to...
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