# Does the resistance of a wire vary with length?

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Introduction

Does the resistance of a wire vary with length?

To find out whether the resistance of a wire varies with length, I will set up a circuit and discover how changing the wires length, changes its resistance too. This experiment aims to investigate how the resistance of a wire increases when the wire length increases.

Background Information:

Current is the flow of electrons round a circuit, and the voltage is the driving force that pushes the current round. The resistance is anything in the circuit which slows the flow down. If you increase the resistance of a circuit, then less current will flow. The variables that effect the resistance of a piece of wire are; temperature, diameter, type of alloy and the length. In metals the current is carried by electrons. Resistance is measured in ohms. The equation of Ohm’s Law is V = I x R. The potential difference is the same as the current multiplied by the resistance.

Atomic Theory:

Metals contain a ‘sea’ of electrons which flow throughout the metal.

Middle

Prediction:

I predict that the longer the wire is the more resistance their will be. I will be interested to find out from my results whether the distance is directly proportional to the length. In physics, the atomic theory is a theory of the nature of matter. It states that all matter is composed of atoms. The theory applies to the common phases of matter, namely solids, liquids and gasses. I believe that if a wire is longer then there will be more atoms for the electrons to have to pass by, therefore increasing the resistance. A shorter wire will have fewer atoms, and less resistance than a longer one. Also, Ohms Lawstates that Voltage is proportional to the Current in a circuit and so a graph showing Voltage against Current should give a straight line. This will show that as length increases, so does the resistance, and if you double the length of a wire, you are doubling the resistance also.

Method:

- Set up a circuit like the one shown below.

Conclusion

While carrying out my preliminary investigation, I have learnt that during experiments, I must keep the voltage low as the wire may melt otherwise. Also I must not let the wire touch the resistor by accident, as this increases the Amp and Voltage reading, and will make the experiment results inaccurate. These factors will help me to plan future experiments and collect better and more accurate results.

From the graph I can obtain the resistance from the gradient. A straight line is y=mx+c, m being the gradient and c being the intercept. Resistance is equal to the inverse of the gradient on a current verses voltage graph, and in Ohms Law R = V/I and on a Voltage by Current graph, the resistance is the gradient.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

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