Investigating the factors effecting resistance of a wire

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Investigating the factors effecting resistance of a wire

Introduction

I am going to investigate the factors effecting the resistance of a wire.

This happens because of the electrons that flow through the wire. These electrons travel at a steady pace, when they come to a different piece of wire, they have to slow down in order to be able to pass. (This is why the current differs). While moving through the wire, the electrons need to squeeze together. This is because there is not enough room

Ohm's law states that the current flowing through the circuit is directly proportional to the voltage applied. (If you double one, you double the other.)

Electricity is conducted through a conductor, in this case wire, by means of free electrons. The number of free electrons depends on the material and more free electrons means a better conductor, i.e. it has less resistance. For example, gold has more free electrons than iron and, as a result, it is a better conductor. The free electrons are given energy and as a result move and collide with neighbouring free electrons. This happens across the length of the wire and thus electricity is conducted. Resistance is the result of energy loss as heat. It involves collisions between the free electrons and the fixed particles of the metal, other free electrons and impurities. These collisions convert some of the energy that the free electrons are carrying into heat.

Metals conduct electricity because the atoms in them do not hold on to their electrons very well, and so creating free electrons, carrying a negative charge to jump along the line of atoms in a wire. Resistance is caused when these electrons flowing towards the positive terminal have to ‘jumps’ atoms. So if we double the length of a wire, the number of atoms in the wire doubles, so the number of jumps double, so twice the amount of energy is required: There are twice as many jumps if the wire is twice as long.

The thinner the wire is the less channels of electrons in the wire for current to flow, so the energy is not spread out as much, so the resistance will be higher: We see that if the area of the wire doubles, so does the number of possible routes for the current to flow down, therefore the energy is twice as spread out, so resistance might halve

Resistance is measured in ohms. The symbol for an ohm is . A resistor has the resistance of one ohm if a voltage of one volt is required to push a current of one amp through it.

Aim

My aim is to investigate the factors effecting the resistance of a wire and to find the factor that effects the resistance of the wire the most and the least.

Variables

Input:

  • Length of wire. *
  • Material of wire.
  • Width of wire.
  • Starting temperature of wire. 

 

Output:

  • The resistance of the wire
  • Voltage across wire.
  • Current in circuit.
  • Temperature of wire. 

 

The variable marked with a * will be varied, the other input variables will be kept constant. The output variable marked with a † will be measured.

1.Temperature : If the wire is heated up the atoms in the wire will start to vibrate because of their
increase in energy. This causes more collisions between the electrons and the atoms as
the atoms are moving into the path of the electrons. This increase in collisions means that
there will be an increase in resistance.
2.Material : The type of material will affect the amount of free electrons which are able to flow through
the wire. The number of electrons depends on the amount of electrons in the outer energy
shell of the atoms , so if there are more or larger atoms then there must be more electrons
available. If the material has a high number of atoms there will be high number of electrons
causing a lower resistance because of the increase in the number of electrons. Also if the
atoms in the material are closely packed then the electrons will have more frequent collisions
and the resistance will increase.
3.Wire length : If the length of the wire is increased then the resistance will also increase as the
electrons will have a longer distance to travel and so more collisions will occur. Due to this
the length increase should be proportional to the resistance increase.
4.Wire width : If the wires width is increased the resistance will decrease. This is because of the
increase in the space for the electrons to travel through. Due to this increased space between
the atoms there should be less collisions.

Preliminary Experiment

Method

1.                  One metre length of 0.4mm diameter “constantan” (a metal alloy) wire is fixed to a metre rule.

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2.                  The first crocodile clip is clipped to the wire at the 0cm position on the metre rule.

3.                  The second crocodile clip is clipped to the relevant position depending on the required length of wire.

4.                  The power supply is turned on. The voltage and current are then read off the ammeter and voltmeter, and recorded.

5.                  The power supply is then turned off and the second crocodile clip is moved to the next position.

  1. Collect apparatus: a voltmeter, an ammeter, 5x wires, 2 crocodile clips, 10, 20 and 40 cm of both nichrome and copper wires ...

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