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# Resistance Coursework

Extracts from this document...

Introduction

Resistance

Aim:

In this investigation I want to find out how the length of and the width of the wire affects the resistance.

Resistance:

An explanation of what resistance would be that resistance is the opposition of a                                    conductor to a flow of current. It is when traveling electrons in a wire collide with the atoms of a wire. The collisions between the electrons and the atoms cause the electrons to move slower, which causes resistance. So, resistance would be how hard it is to move electrons through a wire. Resistance is measured in Ohms (   )

Resistance =     resistivity p (ohm metres) x length l

Cross-sectional area A (square meters)*

Current flows through a wire by a flow of electric charges.  Wire is made up of a lattice of positive ions, surrounded by 'free' electrons. Ions can only vibrate about in their fixed positions but electrons are free to move randomly from one ion to another. When the battery is attached to the wire, the free electrons are repelled by the negative and attracted to the positive. They still have some random movement but they move slowly in the same direction through the wire with a steady drift.

Ohm’s Law:

In 1827, a German physicist discovered relationship that the amount of steady current through a large number of materials is directly proportional to the potential difference, or voltage, across the materials. Thus, if the voltage V (in units of volts) between two ends of a wire made from one of these materials is tripled, the current I (amperes) also triples; and the quotient V/I remains constant. The quotient V/I for a given piece of material is called its resistance, R, measured in units named ohms.

Middle

In metals, the outermost electrons are held only very weakly to the atom and often wander away from it and go to the nearby atom or one a bit further away. These wandering electrons are called conduction electrons and the more of these there are, for a given volume of metal, the better the metal will be as a conductor of electricity. When you connect a battery across a wire, one end becomes positive and attracts the conduction electrons, which drift towards that end of the wire. But the electrons have obstacles to face because the metal atoms are jiggling about because of their thermal energy and so the electrons collide with them and are knocked all over. It’s this difficulty that the electrons have in moving along the wire that we call resistance.

Resistance involves collisions of the current-carrying charged particles with fixed particles that make up the structure of the conductors. A resistor is a material that makes it hard for electrons to go through a circuit. Without resistance, the amount from even one volt would be infinite. Resistance occurs when electrons travelling along the wire collide with the atoms of the wire.

The unit of resistance is Ohms and the symbol is:

The higher the resistance, the lower the current. If there is high resistance, to get the same current a higher voltage will be needed to provide an extra push for the electricity.

Some metals have less resistance than others. Wires are always made out of copper because copper has a low resistance and therefore it is a good conductor. The length and width of a wire also has an effect.

A variable resistor alters the amount of current flowing easily, which makes it very useful for speed control or light dimming.

Conclusion

I believed that my investigation and the results are mainly accurate because my investigation was carried out very well. I believe that if I had to use my results as evidence I think they show that the longer the nichrome wire the more resistance and the shorter the less. I assume this because my graph shows at 10cm of nichrome wire there is 0.592(ohms) and at 100cm of nichrome wire there is 2.386(ohms) there is a difference of 1.794(ohms) which proves longer the wire the more resistance. I can prove that my experiment was successful because of the graph I drew. It showed length of wire against resistance.  If I had to further improve my investigation I would carry it out again and I would do it with a much longer piece of wire at a higher current.

If I had to do this experiment again I will probably measure the wire every 5cm’s instead of 10cm’s to make sure it’s accurate and use a more accurate volt meter to get the best and accurate results. . I could also investigate how the diameter of a wire affects the resistance.

An extra investigation I can carry out or perform to receive more proof and evidence would be to investigate and look into is the thickness of a wire and evaluate or match up with the length of the wire. Also I could examine if the specific metal materials or properties makes a change in the resistance.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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