Does a Light Bulb Obey Ohm's Law?

i.e. when the potential difference was 4 volts the current increased by 0.34 amps,

      when the potential difference was 8 volts the current increased by 0.22 amps.

The results can be explained using science.

Variables

The variables in the experiment

Independent variable

I altered this variable.

• Voltage

Controlled Variables

• Length of wire
• Cross sectional area of wire
• Wire Material
• Light Bulb

Fair Test

Controlled Variables

For the interest of a fair test and accurate results, these controlled variable will be maintained and kept constant for each voltage, as they can affect the rate of reaction

• Length of wire. The longer the wire, the further the electrons have to travel, so the more the resistance. The shorter the wire the less the electrons have to travel so the less the resistance
• Cross sectional area of wire. The larger the cross section of a wire, the less struggle for electrons to go past, the lower the resistance. The smaller the cross section of a wire, the more struggle for electrons to go past, the greater the resistance
• Wire Material. Different materials conduct electricity in different ways, the better the conductor, the less the resistance. The worse the conductor, the more resistance.
• The same light bulb, which had the same tungsten filament.

Ohm’s law does not apply to circuits where there are temperature changes. The variable, temperature, meant that ohm’s law could not be applied to the light bulb.

It is the light bulb itself that emits the heat. It’s source is the tungsten filament, as when electrons try to pass through the tungsten filament they collide with the tungsten atoms which induce heat and increase the atoms’ vibration, which leads to further collisions and leads to more light heat and of course resistance. The result supports my Hypothesis.

Evaluation

I believe the investigation was successful as the results produced agree with scientific knowledge.

In the Ohm’s Law coursework I investigated whether or not a light bulb obeyed ohm’s law. In the experiment we progressively increased the potential difference to see how it affected the current flowing through a light bulb.

The experiment was carried out accurately in many ways.

All variables, other that voltage, the independent variable and temperature, were kept at a constant.

The results were handled with accuracy.

The results were plotted on a graph. A line of best fit was put on each result which meant the results are very accurate, rather than being rounded.

The method in which the Ohm’s Law investigation was carried out is sufficient enough to support a firm conclusion, this is because:

All variable, which effect resistance, were controlled and maintained. With the exception of, voltage, the independent variable and temperature, all were kept constant.

For the interest of a fair test and accurate results, these controlled variable will be maintained and kept constant for each voltage, as they can affect the rate of reaction

• Length of wire. The longer the wire, the further the electrons have to travel, so the more the resistance. The shorter the wire the less the electrons have to travel so the less the resistance
• Cross sectional area of wire. The larger the cross section of a wire, the less struggle for electrons to go past, the lower the resistance. The smaller the cross section of a wire, the more struggle for electrons to go past, the greater the resistance
• Wire Material. Different materials conduct electricity in different ways, the better the conductor, the less the resistance. The worse the conductor, the more resistance.
• The same light bulb, which had the same tungsten filament.

Voltage was supplied with an accurate variable d.c. supply. Current was measured using an accurate ammeter and voltage was measured with an accurate voltmeter.

For further accuracy I conducted the experiment twice so I could work out the average. Both times the results were expected and were very similar. Therefore I believe that this investigation has sufficient evidence to support a conclusion that a bulb does not obey ohms law. A bulb is a non ohmic conductor.

If I were to repeat the investigation I would improve it by

• Using other conductors like lasers.
• Made the length of the wire into a an independent variable
• Made the cross section area of the wire into an independent variable
• Made the material of the wire into an independent variable
• Made the type of bulb into an independent variable

Although I believe my investigation to be a success I believe if I were to make the improvements I said, I would have reliable results with an even stronger conclusion as a wider range of information would have been taken into account