Resistance

GCSE: Physics

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Fair testing:
To achieve a fair test, I will have to keep certain factors constant whilst one key variable is changed. This will provide me with a varied set of results, which I can analyse and conclude in the coming sections. When non-variables are altered in any way, the experiment would not be a fair test and hence I will not fulfil the aim of the experiment. . In order to do this, I have looked at all the possible factors that can affect the resistance of a wire.
I will make sure that I wait for at least 2 minutes before recording any results and that the result in the graph are checked for anomalies, the crocodile clips were all placed at the edge of the meter ruler.
Controlled Variables
There are various control variables for this experiment. If these are not kept constant throughout the experiment, they can affect the dependent variables (resistance of the wire). These include:
Material of the wire:
Temperature
Cross sectional area
Length of the wire
Dependent Variable
Resistance: This is dependent upon the independent variable; the length of the wire. Resistance would not be measured directly, as I do not have an apparatus available that would allow me to measure the resistance automatically. To calculate the resistance, I will use ohms law:
Resistance (Ω) = voltage (V) ÷ current (A)
Strain- more strain more resistance
Strong magnetic field increases the resistance
More light increases the resistance of a wire
Independent Variables
Thickness of wire- This is the crucial factor of my investigation. The thicker the wire, the lesser the resistance.
Length of wire- I have altered this variable by using 10 different lengths of wire that have been equally stretched out. The longer the wire, the more the resistance. This would provide me with a varied set of results.
Resistance in electrical terms is the opposition to the flow of electric current. It is found by dividing the voltage by its current. Current is measured in amperes/amps with SI units A by an ammeter. Voltage is measured in volts by a voltmeter with the SI unit V. Voltage is a measure of the energy required to move a charge from one point to another. Voltage is the A difference in the amount of electric charge between two points creates a difference in potential energy, measured in "volts," which causes electrons to flow from an area with more electrons to an area with fewer, producing an electric current. Current is flow of electric charge, this was earlier suggested by ohms hence the standard units for resistance is ohms with symbol Ω. Therefore the general formula for finding resistance is:

Where R is the resistance, V is the voltage and I is the current. From this formula we can also derive that current is directly proportional to voltage but inversely proportional to resistance therefore the voltage: current graph must be a straight line graph with a strong positive correlation just like the one below but at a constant temperature:







From the graph below, we can see that with a great gradient we have a great current and the same for the voltage. This graph respects ohms law. Doubling the voltage means doubling the temperature. This is because when there is more voltage to aid the flow of electric charge, the electrons flow very easily and hence less resistance. A resistor has the resistance of one ohm if a voltage of one volt is required to set in motion a current of one amp through it. A resistor is everything that can oppose the flow of electric current in my circuits but in this experiment I have used different resistors for different tests. Therefore the degree of opposition given by a resistor is the resistance of a wire. Just for a common example, in a light bulb filament, the long thin wire (tungsten) resists the flow of electrons thereby dissipating electrical energy into heat and light.
There are many factors that affect the resistance of a wire and therefore to ensure the effectiveness of my actual investigation, I have looked at them individually to find the most suitable measures to use. These include:
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