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Investigating the Resistance Of A Light Bulb As The Voltage Is Increased.

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Neil Fraser        Science        Mr Fox

Investigating the Resistance Of A Light Bulb As The Voltage Is Increased.


Resistance is the confrontation of electrons flowing through an electrical component. The resistance slows down the flow through the component, due to the friction created. The current in a circuit gets smaller the bigger the resistance is.

To work out resistance you can use this formula:

  Ohm’s Law – R= V           (Resistance = Voltage/ Current)


To measure the resistance in a circuit you would need to find out what the voltage and the current is in the circuit. To find the voltage of a light bulb in a series circuit and hence the voltage of the circuit you would need to use a voltmeter, which would be connected in parallel with the light bulb to find the voltage across the bulb. (See diagram below).

Then you would need to find the current in the series circuit by placing an ammeter in the circuit, which would give you the current of the circuit as well as the bulb current. (See diagram below.)

To find the resistance of the circuit, you would then divide the voltage by the current.

For this experiment I will be using a series circuit rather than a parallel circuit.

...read more.


The diagram below shows inside a piece of wire showing the free electrons-the flow- and the metal ions. If the temperature is increased then the free electrons in the diagram will hit the metal ions more creating more resistance. If the thickness of the wire was changed i.e. when the metal is thinner the free electrons will have a smaller area to pass through and will hit the metal ions more and so there is greater resistance, than in a thicker wire where there is a greater area for the electrons to pass through. Therefore it will be easier for the free electrons to move through a thicker wire and the resistance is therefore lower.

I believe that if the Voltage and/or the current are increased then the light bulb filament will get brighter and the resistance will go up because the temperature changes. This breaks ohms law as the temperature changes so therefore the resistance will change. You can tell that the temperature rises because of the colour of the light bulb filament. If the light bulb filament is an orange colour at around 2 volts

...read more.


These results show that if the resistance on the resistance graph is too high it will then be lower on the current graph.

I think that some results are wrong due to the rheostat being unreliable. One reason for this could have been that the rheostat could have had a loose connection. Also the coiling of the wire in the rheostat could have become pulled apart with use and this could make the rheostat inaccurate. I tried to avoid this by checking if any rheostats worked better but they did not work as well. To have solved this the school could have had some new rheostats.

My results were good enough to support the prediction and for this reason I think my investigation was worth carrying out.

Further work to this experiment could have been done with a new reliable rheostat which would give me more accurate results. Also I could have changed the make of the light bulb to see if a different make of light bulb would have given similar results and verified the prediction. Using a different light bulb may give different results as the metal filament may be different but the general pattern should be the same.

...read more.

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