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### Investigating the Resistance Variation of Filament Bulbs

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Investigating the Resistance Variation of Filament Bulbs

Circuit Diagram

[IMAGE]

Apparatus

Power supply To provide the power (in 3-12 volts)
-------------------------------------------------

Variable Resistor To adjust the current to get the most suitable
values

Filament bulb To investigate the resistance variation in a 6v, 0.06A
bulb

Ammeter To measure the current through the bulb (up to 10A, 2 decimal
places)

6 Connecting wires To connect the circuit

Voltmeter To measure the voltage across the bulb (up to 20V, 2 decimal
places)

Safety

· Don't have a current to large as it can damage the equipment

· Avoid a short circuit

· Switch apparatus off if it becomes too hot

· Don't go near electrical equipment with wet hands

· Be careful with equipment

Fair Test

To keep this experiment a fair test I will use the same apparatus and
the same bulb, because results may differ with other equipment, so by
using the same I am avoiding anomalous results.

Reliability

I will do the experiment twice so I can compare the results to see if
the trends are the same and avoid anomalous results.

Method

The first thing I will do is collect all of my equipment. I will then
connect the equipment to make the circuit. Next, I will measure the
current (in amps) through the bulb and the potential difference (in
volts) across the bulb. To get a good range off results I will change
the voltage of the power supply (from 3-12V) and move the variable
resistor. After doing this experiment once I will then wait for my
apparatus to cool down and do it again. I will then record my results
and find the resistance of the bulb by dividing the potential
difference by the current. From my results I will draw a graph with
two lines, one being my first experiment and the other my second. This
way I will be able to see how reliable my results are.

Prediction

I think when the bulb starts to get hotter the molecules in the bulb
with vibrate faster, so it will be harder for the molecules to get
through, therefore the resistance will increase. The resistance of the
bulb at normal temperature is 6V/0.06A, which is 100 ohms, so if the
filament bulb gets colder this will decrease, however if gets hotter
it will be more than 100 ohms. Before doing the experiment I found out
a resistor graph is a diagonal, positive straight line, when at a
constant temperature, so if the temperature increases the gradient
will get less steep, this is what I expect my graph to look like.

Investigating the Resistance Variation of Filament Bulbs

Results Table

P.D.

(V)

Current

(A)

Resistance

(Ohms)

P.D.

(V)

Current

(A)

Resistance

(Ohms )

1.54

0.03

51.33

1.48

0.03

49.33

2.41

0.03

80.33

2.33

0.03

77.67

3.53

0.04

88.25

3.42

0.04

85.50

4.30

0.05

86.00

4.35

0.05

87.00

5.46

0.05

109.20

5.38

0.05

107.60

7.75

0.06

129.17

7.76

0.06

129.33

7.83

0.06

130.50

7.84

0.06

130.67

9.44

0.07

134.90

9.45

0.07

135.00

12.62

0.08

157.75

12.63

0.08

157.88

Analysis

When the bulbs received more current the molecules in the bulb
vibrated fast and the bulb became warmer as the resistance increased.
As the voltage increased the current and resistance did also.

The resistance of the 6V bulb increased as the current and voltage
did. However, in the pure resistor trial experiment the resistance
stayed around the same as the current and voltage increased.

The difference between the bulbs and trial experiment graphs are that
the bulb graph was a straight line with an increasingly deeper
gradient and the other was directly proportional to the voltage. The
reason the bulb graph curved is because as the bulb became hotter the
molecules vibrated more, so the resistance increased. I have circled
the anomalous result on the graph and found that the anomalous results
in my first experiment were the same as in my check experiment. This
shows that my results are reliable.

The trial experiment graph obeys Ohm's Law because it is directly
proportional but my bulb experiment doesn't.

My conclusion supports my initial prediction as the resistance did
increase and the results made a graph with a positive straight line

with a gradient which less steep.

Evaluation

I think my evidence is reliable because the anomalies in my first
results were the same as the ones in my second results. The graph made
a straight line with a gradient that gets deeper that is what I
predicted. To improve my experiment to make it even more reliable I
could use a more accurate ammeter and a larger range of results as
well as more checks. The ammeter I use could be more than two decimal
places, and I could get a lot of results and put them on one graph to
make my results are reliable and I have a good accurate graph.

Further Work

Apparatus

Power supply To provide the power (in 3-12 volts)
-------------------------------------------------

Variable Resistor To adjust the current to get the most suitable
values

Filament bulb To investigate the resistance variation in a 12V, 2A
bulb

Ammeter To measure the current through the bulb (up to 10A, 2 decimal
places)

6 Connecting wires To connect the circuit

Voltmeter To measure the voltage across the bulb (up to 20V, 2 decimal
places)

Safety

· Don't have a current to large as it can damage the equipment

· Avoid a short circuit

· Switch apparatus off if it becomes too hot

· Don't go near electrical equipment with wet hands

· Be careful with equipment

Fair Test

To keep this experiment a fair test I will use the same apparatus and
the same bulb, because results may differ with other equipment, so by
using the same I am avoiding anomalous results.

Reliability

I will do the experiment twice so I can compare the results to see if
the trends are the same and avoid anomalous results.

Method

I will use the same method as my previous experiment but this time I
will

be using a 2A bulb.

Prediction

I predict that when the voltage reaches 12V the resistance will reach
6

Ohms. This is because the bulb usually works at 12V and it is a 2A
bulb, if you dived 12V by 2A you will get 6 ohms. Another thing I will
predict is that the graph will be a curve like in my graph from the
first experiment. The resistance will increase, as the bulb gets
hotter like in the first experiment also. Therefore when the voltage
is less than 12V the resistance will be less than 6 ohms.

Results

P.D.

(V)

Current

(A)

Resistance

(Ohms)

P.D.

(V)

Current

(A)

Resistance

(Ohms)

2.85

1.01

2.82

2.95

1.03

2.86

4.15

1.21

3.43

4.15

1.21

3.43

5.15

1.42

3.63

5.70

1.41

4.04

7.03

1.57

4.48

7.01

1.58

4.44

8.50

1.73

4.91

8.55

1.75

4.89

11.41

2.03

5.62

11.34

2.03

5.59

Analysis

When the bulb received more current the molecules in the bulb vibrated
faster and the bulb became warmer as the resistance increased. As the
voltage increased the current and resistance did also. The resistance
of the 12V bulb increased as the current and voltage did like in the
first experiment and made a curve on the graph like I predicted. I
found that the results from the first experiment follow the same
pattern as the ones in the second. The reason the bulb graph curved is
because as the bulb became hotter the molecules vibrated more, so the
resistance increased.

Evaluation

Overall I found that when you use a 12V bulb instead of a 6V one the
trend is very similar. The results make up a similar graph and the
resistance increases, as the bulb gets hotter. Looking at my graph I
cannot see any anomalous results and think they are very reliable. To
improve my experiment to make it even more reliable I could use a more
accurate ammeter and a larger range of results as well as more checks.

MLA Citation:
"Investigating the Resistance Variation of Filament Bulbs." 123HelpMe.com. 10 Dec 2013
<http://www.123HelpMe.com/view.asp?id=147817>.