To make my experiment a fair test I will have to make sure I keep many things the same. First of all, the power pack; I will have to use the same power pack for each test as they will all give out slightly varied voltages to each other. I will also have to use the voltmeter to judge how much voltage is coming out as the power pack dial is more than likely inaccurate. In addition, I must use the same light bulb as each bulb will have a slightly different resistance, therefore giving us a different current reading.
I will also need to keep the same volt meter and ammeter as they will vary in sensitivity. Finally, I will keep the wires the same as (like the bulb) they will have slightly different resistance values. Key Variables: The key variables that could alter my results are the equipment and atmospheric conditions. The temperature of the room and bulb will affect my final results, as temperature affects the resistance of a component. The hotter the component, the higher the resistance. Broken links (for example broken wires) will drastically change my results as the circuit will not even work. Prediction:
My prediction for my experiment is that the higher the current is, the higher the voltage will be. Ohms law states that: V (voltage) = I (current) x R (resistance) This means that the voltage and the current should be in proportion, when one is increased. Because of this, we can estimate what the graph should look like: The graph shows that the voltage goes up in proportion to how much current there is. But I predict that the resistance of the bulb will not change throughout the experiment. However as the filament is used for a longer period of time, the filament inside the bulb will get hotter.
How resistance is caused: It is stated in the particle theory that as molecules and atoms are heated, they will begin to vibrate. Its vibration will cause the resistance to increase by scattering the electrons so that less electrons can get through. So the hotter the filament gets, the higher the resistance. In theory, this should cause the light bulb to slowly stop increasing in current due to the resistance, as shown in the graph below. The line will curve and level out as the temperature of the bulb stabilizes. This will have an effect on the voltage and current.