# Is a Filament Bulb an Ohmic Resistor?

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Is a Filament Bulb an Ohmic Resistor?

First of all I did some research because to answer the question 'Is A
Filament Bulb an Ohmic Resistor' I needed to know what an ohmic
resistor was.

OHM'S LAW

The current flowing through a metallic conductor is proportional to
the potential difference. This is only true when the temperature is
constant.

If you read the current as you change the potential difference across
a conductor the ratio V/I (volts over amps) is the same if it is
ohmic.

From digitalbrain.com
---------------------

An ohmic resistor is a component in which Ohm's law is satisfied.

[IMAGE][IMAGE][IMAGE][IMAGE][IMAGE]

OHMIC

VOLTS

[IMAGE] NON OHMIC

AMPS

Preliminary Experiment: Resistance through a wire
=================================================

In this experiment we used a meter stick with wire running down it to
measure the resistance at different distances to decide whether
resistance increases over distance. We changed the voltage or
potential difference 10 times at each length, but in the results table
and graph I have only used the first result from each measurement.

APPARATUS

Meter stick mounted with wire

1 Ammeter

1 Voltmeter

Wire

1 Variable resistor

Crocodile clips

METHOD

1. Attach the ammeter and the voltmeter to the meter stick and
variable resistor.

2. Connect the variable resistor to the power supply and the meter
stick.

3. Plug power supply into the mains and switch on.

4. Check that the voltmeter is showing positive.

Length-cms

Amps-I

Volts-Potential Difference

Resistance-Ohms

0

4.85

0.04

0.008247423

10

2.38

0.46

0.193277311

20

2.08

0.67

0.322115385

30

2.38

1

0.420168067

40

2.2

1.22

0.554545455

50

1.95

1.49

0.764102564

60

MLA Citation:
"Is a Filament Bulb an Ohmic Resistor?." 123HelpMe.com. 22 Sep 2019
<https://www.123helpme.com/view.asp?id=120365>.

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[IMAGE]

So at the end of the preliminary experiment I can say that wire is not
an ohmic resistor, as the resistance is not constantly increasing
throughout the graph other wise we would have a positive gradient and
would be a straight line.

Second Experiment: The Filament Bulb

PLAN

In this experiment I will have one independent variable, this will be
the potential difference or voltage. I will also have two dependant
variables the amps and the brightness of the bulb. I am going to be
investigating whether a filament bulb is an ohmic resistor. The
potential difference or voltage will be controlled using a variable
resistor. We shall take twelve results for each component, with no
retakes, as we do not have enough time.

PREDICTION
==========

I predict that the filament lamp will not be an ohmic resistor, as the
temperature cannot be kept constant through a bulb. The brighter the
bulb is the more heat will be released. As the definition of Ohm's law
depicts it only works when the temperature is constant. So, because of
this the graph will be curved to show a non-ohmic resistor. I expect
the amps to increase as the voltage does as well as the resistance, so
I expect the graphs to have a positive gradient. After the bulb has
been lit there will be a steep gradient on the graph, but after a
while the gradient will become less steep and slowly the graph will
start to become horizontal, as the resistance will not be increasing
at a constant rate.

APPARATUS

1 Filament bulb

1 variable resistor

1 Amp meter

1 Voltmeter

Wire

1 Power pack

Crocodile clips

METHOD

1. Connect the ammeter to the filament lamp and the voltmeter as well.

2. Then connect them to the variable resistor.

3. Then attach the power pack to the variable resistor.

4. Then plug the power pack into the mains supply

Amps

Potential Difference

Resistance

Ohms

1

0.73

2.13

2.917808219

2

0.89

2.89

3.247191011

3

1

3.77

3.77

4

1.15

4.82

4.191304348

5

1.37

5.87

4.284671533

6

1.38

6.78

4.913043478

7

1.48

7.68

5.189189189

8

1.58

8.75

5.537974684

9

1.67

9.69

5.80239521

10

1.74

10.6

6.091954023

11

1.85

11.64

6.291891892

12

1.92

12.55

6.536458333

5. Check that the voltmeter shows a positive reading.

RESULTS TABLE

RESULTS GRAPH
=============

[IMAGE]

CONCLUSION

In conclusion the results graph proves that a filament bulb is not an
ohmic resistor as the gradient changes in steepness a various points.
This proves that the increase in resistance was not constant;
otherwise the line would have been straight. I believe that filament
lamps aren't ohmic resistors because of the heat generated by the
bulb. I think this because if the bulb is generating heat then the
heat cannot be kept constant throughout the experiment. And as Ohm's
law says, 'this is only true when the temperature is kept constant.

EVALUATION

This experiment was carried out relatively fairly but was far from
perfect. We had a suitable method, which enabled us to retrieve
results that I believe to be fair. If I were to do this experiment
again I would make several alterations. First of all, I would use a
more precise ammeter that can measure in Millie-amps, as this would
give me the opportunity to get more accurate results and a more
accurate reading of current. Also, I would do the experiment several
times over to allow us to take an average for the results to prove
them to be reliable. But there is one thing that cannot be improved
upon, and that is human error. Some of the results may have been off
due to human error and there is no way to eliminate human error from
an experiment.