What factors influence the resistance of a wire?
Aim: To devise and carry out an experiment to show how one factor influences the electrical resistance of a wire.
Plan
Factors
The factors which affect the resistance of a wire are:
- Length of wire
- Diameter of wire
- Temperature
- Material of the wire
- Current in the wire
Background information
Resistance is a force which opposes the flow of an electric current around a circuit so that energy is required to push the charged particles around the circuit. The circuit itself can resist the flow of particles if the wires are either very thin or very long. If the resistance in a circuit is high then a lot of energy is used up getting the current through. This energy is mainly changed into heat. An electric heater uses this to produce heat. Another use of resistors is to protect delicate electronic components. If you want to keep the current small to avoid damage, you put a resistor in the circuit with the component. The resistor makes it harder for current to flow and so less will flow. The unit of resistance is the ohm symbol Ω large resistances are measured in thousands or millions of ohms.
In an electrical circuit it is the resistors not the wires, connecting them to the battery that gets hot. Electrons get pushed around the circuit by the battery and they collide with the atoms in the resistors. Energy is given to the atoms so that they vibrate faster – this means that the resistor is getting hotter.
To find the resistance in a wire or circuit the following formula is used:
Resistance (R) = Pd across resistor in volts (v)
Current flowing through it (I)
Also written as
R = V
I
A resistor has the resistance of one ohm if a voltage of one volt is required to push a current of one amp through it. George Ohm discovered that the emf of a circuit is directly proportional to the current flowing through the circuit. This means that if you triple one, you triple the other He also discovered that a circuit sometimes resisted the flow of electricity. He called this resistance.
Prediction
There are various factors that affect the resistance in a wire; this includes the length of the wire. The length of a wire will affect the resistance because wires have a net of atoms and the electric current has to pass through this net. Every time a charged atom hits the net it loses some of its charge, therefore the longer the wire the larger the chance of the charged electrons colliding with the net and losing some of their charge therefore increasing the resistance. So I predict that if there is a long length of wire there will be more atoms to collide with so the electrons will be slowed down more. If you double the length of the wire, you double the number of atoms that can hinder the movement of the current carrying electrons. In other words you double the resistance. When put mathematically, this means that the resistance of the wire is directly proportional to its length. Therefore the resistance will be higher on a longer wire than a shorter one. Another factor which affects the resistance in a wire is the diameter of the wire. Ohms law states that if the cross section of the wire is uniform then the resistance is proportional to the length and inversely proportional to the area of the cross section. Therefore I predict that the diameter of the wire will have an affect on the resistance of a wire. This is because the electrons have to squeeze together more to pass through a thin wire than they do to pass through a thick wire. The type of material will make a difference in the resistance in a wire because the electrons have to pass through the material. These electrons find it easier to pass through some materials than others. For example I know that electrons have to squeeze together more in order to be able to pass through nichrome wire than they do in order to pass through copper wire, this is because the electrons bump together more in nichrome, therefore making the resistance higher. The temperature of the wire would affect the resistance because as the wire gets hotter the atoms begin to vibrate because they are given more energy; this therefore makes it harder for the charged electrons to get through the wire without colliding with the atoms which causes resistance. Therefore the higher the temperature the higher the resistance. Another factor which will affect resistance in a wire is the current in the wire. I predict that the more current flowing through the wire, the higher the resistance, this is because there are more electrons flowing though wire so they are having to squeeze together more than if there was not very much current flowing through. So the electrons would hit the sides more often and loose more energy, therefore causing the resistance to be higher.
