The aim of this investigation is to see what the relationship between voltage, current and resistance is. We will be conducting two different experiments investigate Ohms law, V=I. R using, in our first experiment wire thickness as our input variable. In our second experiment, we will use wire length. In each, we will record the Voltage and current running through the circuit and use this information to work out wire resistance. Background information Voltage: Voltage is Current: Current is Resistance: Resistance is a measure of how much the current in a circuit is slowed down.
Resistance is caused when electrons have to’jump’ from one It is measured in Ohms (? ) Ohms law Electrons Introduction Hypothesis- the thicker or shorter the wire the easier it is for current to flow round the circuit so more current flows through the circuit and so the smaller the resistance (R = I. V) I have formulated this hypothesis due to my knowledge of the flow of electric current through a circuit.
As seen in my background information I predict that if I plot a graph of Resistance against wire thickness for my results I will get a graph similar to the one bellow A table to show which variables we will need to control in order.
For this to be a fair test and which ones we will measure: Experiment one: wire thickness Experiment two: wire length Input variable Control variables – for a fair test Outcome variable Variable Range interval Variable Value Variable Wire thickness 0.
mm- 2. mm Length of wire 10cms Current Setting of resistor Constant Type of wire Nickel Chrome Supply Voltage Input variable Control variables – for a fair test Outcome variable Variable Range interval Variable Value Variable Wire length 4cms Width of wire Current Setting of resistor Constant Type of wire Nickel Chrome Supply voltage Preliminary experiment.
Doing a preliminary experiment is necessary when doing any investigation because it allows us to plan which variables and ranges will be suitable for use, for our actual experiment to give us reliable results. Method for preliminary Preliminary results Experiment one Wire thickness Voltage Current Resistance The gradient of this graph represents mass, so this shallow gradient shows that the mass must be large. Evaluation of preliminary experiment Our preliminary experiment shows us that we will be able to use this range of values for our final experiment since they gave us results that were relatively consistent with our hypothesis.
Equipment needed: Different lengths of Nickel Chrome (nichrome) wire(experiment two) Different widths of ! 0 cm long Nichrome wire (experiment one) Ammeter Variable resistor Voltmeter Power pack wires Crocodile clips Pulley Method for final experiment A table of results from the experiment: Processing results Preliminary results Actual results Analysis Conclusion: Our findings do appear to have followed what we said in our hypothesis and seem to show the relationship that we predicted, but more experimentation is needed to prove conclusively.
We can definitely see, from our graph that the relationship between wire length and Resistance is, as we said a positive, proportional one, as the wire length increases, the resistance increases. This relationship shows a relatively proportional graph because when you increase the length of the wire there are more atoms in the wire, this means than in order for electrons to flow they must pass between these atoms, the fewer atoms the electrons jump between the less opposition there is to them in the circuit.
What’s more, they bump into each other less, and so don’t create friction and loose their energy as heat. If the electrons are loosing less of their energy then the resistance for a particular voltage must change ( V=I. R) and must get smaller because there is a bigger current to go into the equation. The conclusion reasonably supports the prediction because all of the results that we collected follow the pattern we expected. Analysis Evaluation ResistanceResistance is measured in Ohms (symbol ? ). Resistance The bigger the resistance, the smaller the current.
The very important equation V = I x R is an expression of Ohm’s Law. You MUST KNOW this equation for the exam! If the resistance of a component is constant (stays the same) for different values of V and I, then a plot (graph) of V against I will be a straight line. The gradient (slope) of the line shows how big the resistance is. A test circuit is used to find a range of voltages and currents for a component.
Components which obey Ohm’s Law are Wires and Resistors. A component will only obey Ohm’s Law at constant temperature(meaning that the temperature must not change). In reality, an increase in current through a component will change its temperature (the temperature usually goes up), and so Ohm’s Law is only an approximation but it works quite well for many components. The next page shows plots for components which don’t obey Ohm’s Law.
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