Resistance is the force which opposes the flow of electrons through an electrical conductor. Resistance occurs when the negatively charged electrons travelling along the current in the wire collide with the positively charged atoms of the wire. Hence the atoms are the property which opposes the flow of electrons. These collisions slow down the flow electrons, causing resistance. The electrons have to try to avoid, or travel around the atoms, therefore the flow of current is slowed down. The amount, size and density of atoms have an effect on resistance.

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The circuit itself holds some resistance. There are 3 factors which can affect resistance. These are : * The material of the wire  The length of the wire  The diameter of the wire The material of the wire is a very important factor. Different wires contain different numbers of atoms. Some wires have lots of atoms, whereas others have few atoms. A wire that does not easily conduct electricity would be said to be a bad conductor of electricity. An example of a metal conductor that does not easily conduct electricity is called nichrome.

Wires that have many atoms will have a high resistance compared to wires which have a few atoms which have a low resistance. Wires have a high resistance because there is a smaller area for the electrons to pass through, because there are a large number of atoms present in the wire. Large numbers of atoms reduce the amount of area for the electrons to pass through. Also the size of these atoms can change. Some atoms are large compared to others which are small. A wire which large atoms will have a high resistance because there will be a small area for the flow of electrons in the current to pass through.

This will result in the flow of electrons being slowed down, and also more collision between the atoms in the wire and the electrons in the current. The distribution of these atoms also changes. In some materials the atoms are closely packed together in comparison to other materials where the atoms are spread out. Also these atoms will be large and closely packed together. Therefore there will be a smaller surface area for the electrons to pass through. The flow of electrons will be slowed down, and the collisions between the electrons and atoms will be more frequent.

A wire which easily conducts electricity is a good conductor of electricity. An example of a good metal conductor is copper wire The length of the wire is also an important factor. Long wires have more resistance when compared to short wires. The reason for this is in long wires the electrons have a larger surface to cover, which means it will take the electrons longer to travel from one end of the wire to the other. The reason for this is the collisions between the atoms and the electrons will be more frequent because there is a longer length for the electrons to travel therefore this means that there will be more atoms in the wire.

Also the electrons have to squeeze together for a longer length of time in a long wire to be able to pass through the wire, whereas in a short wire the electrons only have to squeeze together for a short time. Long wires have a larger surface area that the electrons have to cover. Short wires have a small surface area that the electrons have to cover. The final factor which affects resistance is the diameter of the electrical conductor. Different types of wires have different thickness. Wires with a large diameter have less resistance compared to wires that have a small diameter which have more resistance.

Wires with a small diameter have a high resistance because when the of electrons are travelling along the wire there is only a small area in which the electrons can pass through. The electrons have to squeeze together in order to be able to pass through the wire. This would cause the flow of electrons to be slowed down to enable all of the electrons to be able to pass through the wire. There will also be more collision occurring. Not just between the atoms and the electron, but collisions between the electrons and other electrons.

Also in thin wires the atoms are densely packed together which causes more collisions between the atoms and the electrons. Therefore the current will be slowed down, which means that the thin wire has a high resistance. Wires with a thick diameter have a low resistance when compared to wires thin wires. The reason for this is, in wires that have a thick diameter there is a larger surface that the current can flow through. Consequently less collisions between the electrons in the current and the atoms in the wire, because there is a larger surface for the current to flow through.