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The aim of this investigation is to discover how the length of a wire affects its resistance.

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Introduction

Finding the resistance of a wire investigation

Aim

The aim of this investigation is to discover how the length of a wire affects its resistance.

Apparatus

  • Power Pack (AC voltage)
  • Ammeter
  • Voltmeter
  • 100cm of Nichrome wire
  • Crocodile clips
  • Circuit Wires
  • Meter Rule

Firstly, I will briefly explain what voltage, current and resistance is.

Voltage- Voltage is a measure of the amount of "push" given to electric charge in a circuit. We nearly always consider electrons as the charges (charge carriers) being pushed around a circuit. If there is no "push", electrons will not be moved around the circuit. This voltage would normally be supplied by a cell, battery or power pack.

Current- An electric current is the flow of charged particles. Inside a copper wire, current is carried by small negatively charged particles, called electrons. The electrons drift in random directions until a current starts to flow. When this happens, electrons start to move in the same direction, toward the positive terminal. The size of the current depends on the number of electrons passing one place per second.

Resistance-Resistance determines how much current will flow through a component. Resistors are used to control voltage and current levels. Resistance is the atoms of a material getting in the way of electrons, as they travel in the direction of the negative terminal. The electrons collide with the atoms.

Ohms law states that if you have one volt applied to a one-ohm resistance, the current will be one amp.

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Middle

Hypothesis

1. I predict that as the length of the wire increases, the resistance will also increase in proportion to it. I have come to this conclusion because of my previous studies of resistance, and because of my preliminary results. My logic is that I know that atoms in all conductors have free electrons in the outer shell of their structure. It is because of this structure that the outer electrons can move freely about. I have shown below in the diagram how the electrons move when there is a potential difference passed through a conductive material.

The atoms are arranged in a honeycomb shape.

The free electrons drift around inside the wire, in the general direction of the positive terminal. This is called the electron drift current. As the electrons drift toward the positive terminal, they collide with the metal atoms that make up the wire. These collisions cause the electrons to move more slowly, which in effect causes resistance. If the length of the wire is increased, then the resistance will also increase as the electrons have will have a longer distance to travel, thus more collisions will occur. Due to this, the length increase should be directly proportional to the resistance of the wire.

2. I also predict that as we increase the potential difference in the circuit, the resistance of the wire will increase. I know that current is directly proportional to P.D (potential difference)

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Conclusion

*The diagram above shows a model of charge moving from a connecting wire to a thinner piece of test wire. The thin wire has less conducting electrons than the same length of connecting wire, and so the charge has to move faster to maintain the same current or flow rate through the thin wire. This should lead to heating of the thin wire, as the electrons transfer their energy in collisions with the metal atoms. The greater the number of collisions, the more energy is transferred as an electron passes through, and the greater the resistance to charge flow.

This is similar to trying to suck milkshake up through a thin straw, or through a thick straw. The milkshake will move more easily up the thick straw, which has a larger diameter. The relationship is one that is "inversely proportional". In other words, there is a direct link between the thickness of the wire, and the loss or resistance, and the larger the area of a cross section of the wire, the lower the resistance.

To keep this experiment fair, I would: use the same connecting wires, submerged the test wire in water, kept the P.D constant, kept the wire material the same and kept the length of the test wire constant.

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