# Investigating the Resistance of a 12 Volt Bulb When the Current Changes

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Investigating the Resistance of a 12 Volt Bulb When the Current Changes

Prediction: I predict that as the current increases the temperature of
the lamp will also increase; therefore the resistance will also
increase. I know this because I have read it in the AQA syllabus.

Plan

Safety: I need to ensure the safety of myself and others by making
sure that the experiment is conducted accurately and safely.

- Apparatus should be placed in a safe place and put away safely.

- Electrical plugs should be switched off after use.

- The area should be kept dry and taps should be switched off.

Variables: I will only be changing the current by moving the variable
resistor.

I will repeat the experiment twice so that I can be sure of my
readings and see if anything has changed or gone wrong. I will take 12

Apparatus:

o Voltmeter

o Ammeter

o Variable resistor

o 12 volt lamp

o Battery pack (set at 12 volts )

Method:

1. Using the apparatus listed above I will set up the following
circuit:

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[IMAGE][IMAGE][IMAGE][IMAGE]Key

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[IMAGE]Variable resistor

[IMAGE]

[IMAGE][IMAGE]Ammeter

[IMAGE]

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Lamp

[IMAGE]

[IMAGE]Voltmeter

[IMAGE]

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[IMAGE][IMAGE][IMAGE]Battery pack

[IMAGE]

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2. 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.

3. I will start with 0.5 amps, working systematically, I will note

MLA Citation:
"Investigating the Resistance of a 12 Volt Bulb When the Current Changes." 123HelpMe.com. 20 Feb 2020
<https://www.123helpme.com/view.asp?id=121004>.

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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.

Fair test: To make this investigation a fair test I will use the same
equipment and the same method every time I repeat the experiment so
that nothing will change. I will also wait until the lamp cools down
so that it is at the same temperature that it was when I first used
it.

Obtaining evidence

A table of my results:

Current (amps)

Voltage (volts)

Voltage (volts)

Experiment 1

Experiment 2

0.5

1

1

0.6

1.5

1.5

0.7

2

2

0.8

3

3

0.9

4

4

1

5

4.5

1.1

5.5

6

1.2

7

7

1.3

8

8

1.4

9

9

1.5

10

10

1.6

11

11

I will now find the average voltage. I will do this u by adding the
voltage for experiment 1 and 2 and then dividing it by 2. Using the
average voltage and current I will find the resistance using the
following formula:

R= V/I

(The resistance has been rounded to 1 decimal place.)

Current (amps)

Average voltage (volts)

Resistance (ohms)

0.5

1

2

0.6

1.2

2.5

0.7

2

2.9

0.8

3

3.8

0.9

4

4.4

1

4.75

4.8

1.1

5.75

5.2

1.2

7

5.8

1.3

8

6.2

1.4

9

6.4

1.5

10

6.7

1.6

11

6.9

Using the results on my table above, I will now draw a graph ( page 5)
to show current against resistance. I will draw a line of best fit.

Graph showing the current against resistance

Analysing and considering evidence

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.

Using my graph I can see that there are two anomalies; the other
results are all close to the line of best fit. These two anomalies are
near the higher end of the graph and are not near the line of best
fit. The reason for these odd results may be because there was human
error involved or factors such as the temperature of the lamp. With
the time that I was given I think that enough results were taken to
support the conclusion.

To help me with my investigation I used the following secondary
resources:

o AQA syllabus

o Modular science for AQA