I R
V= voltage measured in volts
I= current measured in amperes
R= resistance measured in Ohms
Whenever you need to find a missing value, cover it with your finger. The horizontal line in the middle means to divide the two remaining values. The “X” in the bottom section of the triangle means to multiply the remaining values.
E.g.
- If you are calculating the voltage, cover the “V” and you have “I x R” (V= I times R)
- If you are calculating the current, cover the “I” and you have “V divided by R” (I=V/R)
- If you are calculating resistance, cover the “R” and you have “V divided by I” (R=V/I)
Ohms law:
Ohms law states: “The amount of current flowing in a circuit made up of pure resistances is directly proportional to the electromotive forces impressed on the circuit and inversely proportional to the total resistance of the circuit.”
Basically this means that a steady increase in voltage, in a circuit with constant resistance, produces a constant rise in the current.
E.g. If the voltage is doubled the current will also be
doubled.
Superconductors:
There are a small amount of conductors that do not obey ohm’s law... these are called superconductors and below a certain temperature they have absolutely no resistance to a current, because of this no energy is lost and the current can flow forever.
Superconductors have a special, unique propriety known as ‘Superconductivity’ this is a natural phenomenon in certain conductors that have no resistance to the flow of an electric current.
Superconductors also exhibit strong diamagnetism (which means that they are repelled by magnetic fields.) Superconductivity is created only below a certain critical temperature and a certain critical magnetic field, which varies with the material used.
Who is ohm?
Georg Simon Ohm was a German physicist and is famous for his research on electrical currents. He was born in Erlangen in 1787 and died in 1854.
Between 1833 till 1849 he was director of the Polytechnic institute of Nuremberg. Then from 1852 until his death he became the Professor of Experimental Physics at the university of Munich.
He created a formula which explained the relationship between current, electromotive force, and resistance, which is known as Ohm’s law, and is considered the basic law of current flow.
Because of this, the unit of electrical resistance was named the ‘Ohm’ in his honour.
Method
In this experiment we are aiming to find out how changing the length of wire and using different types of wire will affect the amount of resistance produced from our circuit.
To do this we will first have to put together our circuit making sure we connect a voltmeter and an amp meter. This will mean that we are able to measure the changes in volts and amps, and from this data we will be able to work out the amount of resistance produced using the diagram on page 3.
We are going to be using 2 different types of wire in our experiment –Nickelrone and Constantine- to show how different materials give off their own amount of resistance that varies from material to material.
We are also going to be changing the length of the wire by 5cm every time, starting at 15cm and ending up at 40cm. We are starting at 15cm as if we go any shorter the wire can become very hot which would be dangerous and also because it could overload the amp meter which would ruin the equipment and may also lead to us getting unreliable results.
We are also keeping the amount of volts flowing through the circuit the same- 3 volts –because if we use any more this can also make the wire hot and damage equipment.
Results
Nickelrone:
Result 1:
Result 2:
Average result:
Constantine:
Result 1:
Result 2:
Average result:
From these results we can clearly see that the amount of resistance increases, as the length of wire gets longer.
We can also see that the Constantine wire gives off less resistance overall than the wire made of Nickelrone, which completes my aim to prove that different metals give off different amounts of resistance.
These results show us that different metals give off different amounts of resistance, and also that the amount of resistance given off by metals are affected by the length of the wire.
Graphs
Conclusion
This experiment proved that the amount of resistance increased as the length of the wire got longer. This was predicted in my aim, and therefore shows that my prediction was correct.
The results tables and graphs also show us that even if you keep the length of the wires and the amount of volts flowing though the wires the same, each different metal would still have a different amount of resistance.
From this experiment we have learned that resistance is the property of any object or substance that resists or opposes the flow of an electrical current, and the amount of resistance differentiates from substance to substance.
Evaluation
Although this experiment was successful in showing us that resistance increases as the length of the wire’s increases, it still wasn’t completely accurate in its results.
The amount of resistance measured from the wires didn’t rise as smoothly as it should have if the experiment was properly controlled and the apparatus we used was properly maintained and of a higher quality.
These factors could have led to us not getting the highest quality results possible:
- The low quality of apparatus (the amp meter, volt meter, etc…)
- Inaccurate measurements. eg. the length of the wire, the reading from the amp/volt meters, etc…
- Human error.
- Improper handling of the wire. For example if the wire becomes bent or creased it can cause more resistance.
- The low sensitivity of the amp meter.
- The wires may not have been of exactly the same diameter.
I think that we could have furthered our experiment and received better, more reliable results if we made some improvements to the way our investigation was carried out.
We could do this by:
- Using equipment of a higher quality.
- Making sure that wires are not only the same length, but also of the same diameter and hopefully of the same volume.
- Using more sensitive measurements.
