If the number of bulbs in a series circuit is increased, less current will flow. The lamps resist the current, so if you put more lamps into the circuit there is more resistance. As the resistance of the variable resistor decreases the current in the circuit increases until the bulb burns out. The filament of a bulb is a very thin wire and acts as an electrical resistance.
When the current flows, electrical energy is converted into heat and light energy.
Safety:~ I need to ensure the safety of myself and others by making sure that the experiment is conducted accurately and safely. To do this I must ensure the following-
Apparatus should be placed in a safe place and put away safely.
Electrical plugs should be switched off after use.
The area around where I am performing my experiment should be kept dry and nearby taps should be switched off.
Fair Test:~ To make this investigation a fair test I will use the same type of equipment (i.e by using an ammeter instead of a multimeter on the ammeter setting, or a 12V lightbulb instead of a 4V lightbulb) and the same method every time I repeat the experiment so that nothing will change.
Variables:~ The variables that I will be using are: the fixed variable
I will only be changing the current by moving the variable resistor.
I will repeat the experiment so that I can be ensure my readings are correct. I will take 10 readings at 1 volt intervals.
Apparatus:~ For this experiment I am going to use the following apparatus:
Ammeter
Multimeter (using voltage setting)
Variable Resistor
12 volt lamp
Battery pack
Wires
Crocodile clips
Diagram:~
Planned Method:~ I will set up the apparatus as above shown on the diagram.
Results:~
Analysis:~ Looking at the graph I can see that the resistance is directly proportional to the current. This means that as the current increases so does the resistance. For example, when the current is 1.3 amps the resistance is 6.2 ohms. Further on, the resistance is 6.9 ohms when the current has increased to 1.6 amps. This shows an obvious increase in resistance when the current increases.
During the experiment I changed the amount of current so that it increased. The increase in current causes the lamp to get hotter but also means that it will be harder for the current to flow. All solids (including the leads used in the experiment) are made of atoms that are constantly vibrating. The increase in heat gives more energy to the atoms making them vibrate even more. The leads are metal conductors; increased vibrations means that it will be harder for current to flow as the electrons will collide with the vibrating atoms more. The collisions will slow the electrons down; this is resistance.
The resistance of a filament lamp increases as the temperature of the filament lamps increases. Temperature increases with more current. Therefore resistance will increase as the current increases. This agrees with my prediction.
Evaluation:~ I think that the results were accurate as the second experiment showed similar results to the first. This shows that the experiment was carried out correctly and as accurately as possible. To be more sure I could have repeated the experiment a further 2 or 3 times.
To make this experiment more accurate I could have used electronic equipment which would accurately measure the volts and amps so that there would be no human errors. To extend this investigation I could have used different types of bulbs with a different size of maximum voltage. I could have taken more readings, perhaps repeated the experiment a few more times and used a wider range of current.
I will do a preliminary test to find the range of current in amps. I will do this by moving the variable resistor to its lowest and highest points and noting down the amps. In this case the lowest point is 0.5 and the highest is 1.6 amps.
I will start with 0.5 amps, working systematically, I will note down the voltage every 0.1 amps. I will do this until I reach the highest point which is 1. 6 amps. I will then repeat this to see if my results have changed or are the same.
