Sana Javed T11EP
"What affects the resistance of a piece of wire"
In this piece of coursework I have been set the task of investigating the factors that affects the resistance of a wire.
Firstly, 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.
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)*
The factors that effect resistance are firstly, cross-sectional area, for example, a thin wire has more resistance than a thick wire because of the increase in volume of the thick wire. The increase in volume means that there are more electrons flowing.
Secondly, the temperature is a factor, for example in metals a hot wire has more resistance than a cold wire. If a wire is heated, the atoms will move around more because there is an increase in energy. This would cause more collisions between the atoms and the electrons, and the increase in collisions would increase the resistance.
The third factor is materials, because if the material being used has atoms with a large number of electrons this means there are more electrons, so if the material has a large number of atoms there should be less resistance. If the atoms in the wire are closely packed, then this will cause an increase in resistance, because of frequent collisions. The property of materials that compares resistance for unit size is called resistivity p.
Lastly the length of the wire is a factor, as the longer the wire is, the longer it will take for the electrons to get to the end. This is because there will be more collisions between the electrons and atoms. So the length of the wire would be proportional to the resistance. Overall these factors are linked by the formula R=P L/ A
The factor, which I will investigate, will be length. I am choosing length because it is simpler than temperature, cross-sectional and materials.
Prediction
I predict that, the longer the wire is, the more resistance there will be due to more collisions taking place between the electrons/atoms. The length of the wire should be approximately proportional to the resistance. So, if the wire is doubled, then so will the resistance. If the length is twice as much, then there will be twice as much collisions, which would therefore increase the resistance. For example if the length of the wire were doubled then the resistance would also be doubled. If we know the resistivity, the cross-sectional area and the length of the wire we can then calculate the resistance (as shown above). * The resistance of a wire is proportional to its length. There is also the fact that considering the change of current due to more length is the flow of the current as the length has doubled (2 x l) because of this there are twice as many collisions, therefore half as many electrons. Using the formula I= Q/T predicts that the current halves for the same voltage the wire must have twice the resistance as R= V/I. This can be linked to the Ohm's law. The voltage across a metal conductor is proportional to the current through it, provided the temperature stays constant.
"What affects the resistance of a piece of wire"
In this piece of coursework I have been set the task of investigating the factors that affects the resistance of a wire.
Firstly, 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.
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)*
The factors that effect resistance are firstly, cross-sectional area, for example, a thin wire has more resistance than a thick wire because of the increase in volume of the thick wire. The increase in volume means that there are more electrons flowing.
Secondly, the temperature is a factor, for example in metals a hot wire has more resistance than a cold wire. If a wire is heated, the atoms will move around more because there is an increase in energy. This would cause more collisions between the atoms and the electrons, and the increase in collisions would increase the resistance.
The third factor is materials, because if the material being used has atoms with a large number of electrons this means there are more electrons, so if the material has a large number of atoms there should be less resistance. If the atoms in the wire are closely packed, then this will cause an increase in resistance, because of frequent collisions. The property of materials that compares resistance for unit size is called resistivity p.
Lastly the length of the wire is a factor, as the longer the wire is, the longer it will take for the electrons to get to the end. This is because there will be more collisions between the electrons and atoms. So the length of the wire would be proportional to the resistance. Overall these factors are linked by the formula R=P L/ A
The factor, which I will investigate, will be length. I am choosing length because it is simpler than temperature, cross-sectional and materials.
Prediction
I predict that, the longer the wire is, the more resistance there will be due to more collisions taking place between the electrons/atoms. The length of the wire should be approximately proportional to the resistance. So, if the wire is doubled, then so will the resistance. If the length is twice as much, then there will be twice as much collisions, which would therefore increase the resistance. For example if the length of the wire were doubled then the resistance would also be doubled. If we know the resistivity, the cross-sectional area and the length of the wire we can then calculate the resistance (as shown above). * The resistance of a wire is proportional to its length. There is also the fact that considering the change of current due to more length is the flow of the current as the length has doubled (2 x l) because of this there are twice as many collisions, therefore half as many electrons. Using the formula I= Q/T predicts that the current halves for the same voltage the wire must have twice the resistance as R= V/I. This can be linked to the Ohm's law. The voltage across a metal conductor is proportional to the current through it, provided the temperature stays constant.
