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How does length and width affect resistance

Extracts from this document...

Introduction

Aysha Sattar11B

Physics coursework

How does length and width affect resistance ?

Aim

To investigate the resistance of the wire as the diameter and length is altered.

Theory

What are atoms made of?

All materials, solid, liquid or gases are made up of atoms. The atoms themselves consist of a central bit, called the nucleus, made up of particles called protons (which have a positive electrical charge) and neutrons (which have no charge) Orbiting around the nucleus are electrons which are very tiny and have a negative electrical charge. Tiny as atoms are, they consist of even more minute particles.  Each atom has a definite number of these subatomic particles.  The protons and neutrons are crowded into the nucleus, an exceedingly tiny region at the centre of the atom.  If a hydrogen atom were about 6 kilometres in diameter, its nucleus would be no bigger than a tennis ball.  The rest of an atom outside the nucleus is mostly empty space.  The electrons whirl through this space, completing billions of trips around the nucleus each millionth of a second.  The fantastic speed of the electrons makes atoms behave as if they were solid, much as the fast-moving blades of a fan prevent a pencil from being pushed through them.

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A flow of electric charge through a conductor is called electric current.  Energy is associated with the flow of current.  As current flows through electric devices, this energy may be converted to useful forms.  For example, electric energy is converted into heat by an electric cooker and into light by a light bulb.  

Direct and alternating current  

Current that flows steadily in one direction is called direct current (DC).  A battery produces direct current.  Sometimes current flows back and forth, changing direction rapidly.  It is then called alternating current (AC

What is resistance?

...read more.

Middle

Type of material

Different materials have different resistances because the materials' atomic structures are different so some metals have low resistances and some have high resistances. Therefore it is important to keep the material the same throughout the experiment unless a different material is used to check if the conclusion or theory works for all materials. If different materials are used throughout the investigation, it will affect the results. For example if sometimes copper is used and sometimes nichrome is used, the results where copper is used will be of a low resistance because of the material and not because of the diameter or length of the wire. Throughout the experiment Constantan and nichrome will be used. Constantan is used to make sure my conclusion works for all materials. The type of material will affect the amount of free electrons that are able to flow through the wire. The number of free electrons depends on the amount of electrons in the outer 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 of the number of electrons. If the particles in the material are tightly packed together, the electrons will have more collisions and therefore more resistance.

All these factors must be kept constant to make the investigation fair. The same apparatus must be used throughout the investigation. It is also important to take repeats to find an average and see any anomalous results.

Prediction

My hypothesis is that the thinner the wire, the higher the resistance. The thicker the wire, the lower the resistance.

...read more.

Conclusion

Overall, I think the whole investigation went very well. It was successful and gave me the results I needed. It showed me that my predictions were CORRECT.

National Grid

The National Grid is an electricity transmission network of over 5,800km of lines and cables throughout the country. It operates at very high voltages (up to 400,000 volts).

How Does It Work?
At power stations, electricity is transformed to the higher voltage levels of 110,000, 220,000, or 400,000 Volts. It is then fed into a transmission network of 5,800km of overhead lines and underground cables carrying the electricity throughout the country. This network incorporates over one hundred high voltage transformer stations where the voltage is reduced to distribution voltages of 38,000, 20,000 and 10,000 volts. Some larger industrial premises are connected directly at these voltages.

Electricity is distributed at these 'medium' level voltages over an extensive distribution network of 80,000km of overhead lines and underground cables to smaller local substations close to customers' premises. At the local substations, it is finally transformed down to the normal mains voltage level for use by customers.

What are the benefits of a National Grid ?
Power stations do not have to be located in or close to populated areas.

When many power stations are feeding into a grid, the most efficient (and cheapest) stations can be chosen to produce electricity first and only the more expensive plant used when necessary. This lowers overall costs.

Connection to my investigation

The reason that I believe that the national grid is relevant to my investigation is because I know through my own research and from this investigation that thick wires minimize losses of 'low-grade' heat energy. Therefore the wires used in the National Grid system carry very high voltages

And fairly high currents over long distances, so they must be thick in order to minimize losses of 'low-grade' heat energy. As a result, cheap, low-density aluminium is used rather than expensive, high-density copper (although this metal has a lower resistance and so lower losses in conducting electrical energy).

...read more.

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