An Investigation To Show How the Voltage Affects the Current In a Light Bulb
Aim:~ An investigation to show how the voltage affects the current
flowing through a light bulb.
Hypothesis:~ I predict that as the current increases the voltage of
the lamp will also increase; thus causing the resitance to decrease. I
think this because of Ohm's Law which states that current will
increase in proportion to voltage
; if the current is doubled the
voltage is also doubled.
Bearing this in mind my graph should resemble my diagram below:
If the voltage across a light bulb
is increased, more current will
flow through it. If the number of bulbs in a series circuit is
increased, less current will flow through them. 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 bulbs burn out.
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
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
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
* Multimeter (using voltage setting)
* Variable Resistor
* 12 volt lamp
* Battery pack
* Crocodile clips
Planned Method:~ I will set up the apparatus as above shown on the
1st Current (A)
2nd Current (A)
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
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.