Potential difference across the wire (Voltage)
Current through the wire
Potential difference across the wire (Voltage)
Resistance
Current through the wire x Resistance
All resistance is measured in Ohms ( ).
Resistance
There are several different factors that affect resistance to reduce the current in the circuit. These are:-
Material
Different materials can transport electrons through it more quickly than others; therefore different materials are resistors at different levels, depending on which materials are used. This is because different materials have different numbers of free electrons roaming around – the more electrons there are, the more current can would be able to flow at once.
Thickness
If a wire is thick then more electricity can flow at a faster rate and more electricity can flow at once down the wire. The thicker the wire, the faster and larger the current will be. Once again, this is because of the amount of electrons; when the thickness is increased, more area is given to the roaming electrons to move about it, therefore letting them move faster.
Length
If a wire is short, the electricity will quickly travel to its destination and the current in the electrons reaches the end point faster. This means that since the current is transported faster, more of it is transported in a smaller amount of time.
Temperature
When the temperature of a wire is increased, the heat energy gives more energy to the flowing electrons in the wire, causing them to move faster, giving a faster current.
Resistors
There are many different resistors, which are used and activated in different ways, some more useful than others in different scenarios.
Variable Resistor
This is a resistor which can be controlled manually to a certain resistance. They’re usually coils of wire with an adjusting handle bar to specify a resistance. Here you can adjust the length of the wire so the distance the electrons need to travel can be controlled.
Fixed Resistor
The same as a variable resistor, apart from you cannot control the resistance; it has a fixed resistance.
Semiconductor Diode
A diode is made from a semiconductor material (material which conducts less compared to other metals). It stops current going in one direction (making it a direct current).
LED (Light Emitting Diode)
Another diode, so it only allows current to flow in one direction. An advantage of it is that lights are given out when a current passes through it, so you can see when something is actually working or not.
LDR (Light Dependant Resistor)
This resistor reacts on light; when light is present, the resistance falls, and when there is no light the resistance rises in the circuit. It’s useful for automatic night lights, which would turn on when the change of light occurs.
Temperature-Dependant Resistor
It works similar to the LDR, but this one allows higher resistance in cooler conditions and less resistance in warm conditions. This is good for when trying to keep something at a constant temperature – all you would need to do is see the change of a light bulb in a circuit with this resistor to see if the temperatures either increased or decreased.
Experiment on Resistance – different lengths of wire
Conclusion
As we see from the graphs (shown on separate graph paper, Fig.2, Fig.3, Fig.4 and Fig.5), my prediction before the experiment was proven slightly wrong.
If we take the first plot on Fig.2 and the results table, we see that although there is little current and voltage, there is no resistance, meaning that all the current is able to get through, and the voltage is also even so all the current should be able to go through the circuit at normal speed. But if you look at the very last plot on the last graph (Fig.5) and the results table, you can see that although the current and voltage was high, the resistance was three times the size of the voltage and almost forty times the size of the current, so the resistance would easily slow down the current from flowing properly.
This did agree with my prediction, as I had stated that the circuit with the highest variable resistor setting and longest wire would have the highest resistance, and the circuit with the lowest variable resistor setting and shortest wire would have the lowest resistance. This is because with the longer wire, there are much more atoms for the electrons to collide with and cause resistance. Also, there is already more resistance put into the circuit than what there needs to be.
Evaluation
The results, however, are not accurate. The 12cm variable resistor setting did not give us a proper reading on the ammeter and voltammeter, and so we had to change the setting on the power pack from 1 ampere to 5 amperes. Otherwise, the experiment went very well, as we got all of our results as accurately as we possibly could.
We got a few ‘freak results,’ as you can see at resistor setting 6cm and wire lengths 45cm and 50cm, where the resistance has dropped quite a lot compared to resistor setting 3cm and wire lengths 45cm and 50cm. I am not sure how this was obtained, seeing as the resistor setting had increased so the resistance should have as well. It may be that one of the items was not measured accurately.
To improve on my experiment, next time I would definitely make sure that all the power packs and ammeters/voltammeters are set to 5a, so that none will be different. Also, I would use digital ammeters/voltammeters, as they would be more accurate – the needles in the analogue ones can be shook and moved about, giving an inaccurate reading. I would also need to work on a method for giving 100% accurate measuring. To expand on the experiment even further than this, I could involve different widths of wire as well.
