Investigate how the resistance of a wire is affected by the length of the wire.

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Science Investigation

Resistance of a wire coursework

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Aim:        

To investigate how the resistance of a wire is affected by the length of the wire.

Theory

Introduction

Electricity travels through a conductor by means of free electrons. The conductor in this investigation is a nickel wire. The number of free electrons depends on the material of the conductor. The more free electrons there are, the better the conductor due to less resistance. For example, silver has more free electrons than iron; therefore it is a better conductor. The free electrons are given energy and this makes them move and collide with other 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. These collisions convert some of the energy that the free electrons are carrying into heat.

The resistance of a length of wire is calculated by measuring the current in the circuit (in series) and the voltage across the wire (in parallel). The measurements are then substituted into the following formula:

 

V = I * R                (V = Voltage, I = Current and R = Resistance)

 

This can be rearranged into:

 

R = V

      I

The metallic Structure of a conductor

There are three different types of metallic structures; ‘hexagonal close packed’, ‘face centred close packed’ and ‘body centred close packed’. The atoms of the first two types occupy 74% space and the other occupies 68% of the volume. Metal atoms always try to occupy the greatest amount of volume, so they have the smallest gaps. The type of metallic structure a metal has depends on the radius of the atom and the charge it has when it loses its outer (valence) electrons.

The outer (valence) shell electrons of a metal atom are relatively easily removed, with the formation of metal cat ions.

The outer electrons from each atom come under the influence of a very large number of cations. The valence electrons are then free to move through the structure and are no longer in the outer shell of any one atom. This is called ‘delocalised electrons’. The removal of electrons leaves behind layers of cations. The cations repel from each other. They are held in place by the attraction of the cations to the delocalised electron clouds between them.

The relationship between current, voltage and resistance- Ohm’s law

Potential Difference:        This is the work done per unit charge as a charge is moved between two points in an electric field. The potential difference between two points in a circuit is the energy change from electrical into other forms of energy, when one coulomb of charge passes from one point to another. The equation for potential difference is:

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Current: A flow of electricity through a conductor. Current consists of moving electrically charged particles. It is the rate at which electrons flow. The faster they move, the higher the current. The equation for current is:

Ohm’s Law gives mathematical equations, which show the relationship between potential difference, current and resistance in an electrical circuit. The equations are:

V = I * R

R = V / I

 = V / R

Where        V = Voltage

I  = Current

R = Resistance

Ohm’s law states that ...

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