Carry out an investigation of the
relationship between the length
of a metallic conductor (eg
Nichrome Wire) and its
resistance
Introduction
Background research outlined and
referenced
• Firstly I researched this topic in my
science book. I found relevant information
in my book about resistance, such as the
fact that resistance is governed by the
formula V = IR and is measured in
Ohms.
• Ohms can be measured using a
multimeter (O’Callaghan M., Reilly S.,
Seery A., Exploring Science 2003 p86-88)
Background research outlined and
referenced
• Next I found a definition for Resistance on
the internet:
“A force that opposes the flow of an
electrical current around a circuit, so that
energy is required to push the charged
particles around the circuit”
(http://www.sci-journal.org)
Background research outlined and
referenced
• I found out from my Science Teacher that
a metallic conductor is a wire, for example,
copper wire
Investigation is stated as a problem
statement
• During the investigation I intend to answer
the following question
“How does the length of a wire affect it’s
resistance”
Preparation &
Planning
Identification of variables
• Independent Variable:
The LENGTH of the nichrome wire.
• Dependent Variable:
The RESISTANCE of the wire
• Fixed Variables:
TYPE of Wire
SETTING on Multimeter
THICKNESS of Wire
A Fair Test where appropriate is
outlined
• To ensure a fair test, we ensure that the
fixed variables remain the same.
ie TYPE of wire
THICKNESS of wire
SETTING on multimeter
This way, we are sure that when we
change the length of the wire, this and
this alone, will change its resistance.
Resource List Complete
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Length of wire
Pliers
Multimeter
Meter Stick
Safety Glasses
Lab Coat
Connecting wires
Crocodile clips
Plan adequate to test the problem
statement
• The problem statement states:
How does the length of wire affect it’s
resistance.
To plan for this, I must first do a trial run
Trial Run
• Take a length of wire and connect it to the
multimeter using crocodile clips.
• Then take another length and do the
same.
Issues I came across
• Do I start with 1 meter and cut off 10cm
each time……yes
• How do I cut it off…..the pliers wasn’t
sharp enough
• The ends of the wire was kinked…..would
this affect my results….yes (I asked the
teacher)
• What settings do I have on the multimeter
Procedure and
Planning
Safety
• Do not handle multimeter with wet hands
As this may give a shock
• Take care when using pliers to avoid
accidental injury
• Wear safety goggles, as any wire when
cut can recoil backwards and injure
Procedures Listed in Clear Logical
order
•
•
•
•
Gather all apparatus
Put on protective clothing
Set up apparatus as shown in the diagram
Set multimeter to the Ohm setting. Insert
one lead into the COM socket and the
other into the KΏmA socket. Ensure the
claws are attached to the very end of the wire
Procedures Listed in Clear Logical
order
• Ensure that the wire is fully extended
without kinks or loops which would affect
results
• Record this length of wire and it’s
corresponding resistance. To start with we
use 1 meter.
• Now remove the wire and cut off 10 cm
ensuring the ends cut cleanly
Procedures Listed in Clear Logical
order
• Record length and corresponding
resistance.
• Repeat at 80 cm, 70 cm, 60 cm…….10 cm
• Take another 1 meter length and get it’s
resistance at the various length
Recorded Data
Length
/ cm
100
Resistance1 Resistance Total
/Ώ
1 /Ώ
Resistance
1 /Ώ
7.3
7.4
7.35
90
6.6
6.7
6.65
80
5.9
5.9
5.9
70
5.3
5.1
5.2
60
4.5
4.45
4.475
50
3.8
3.8
3.8
Labelled Diagram
Observations
• I did a trial run to get a ‘feel’ for the
experiment
• I did the experiment twice to get the
average
• I made sure that the wire was not kinked
or looped and that the ends were cut
correctly.
Observations
• I noted that the resistance of the wire was
proportional to the length
Graph
•
Ω
Length / cm
Calculations /
Data Analysis
Calculations accurate and clearly
shown
• Data for Table
(Resistance 1 + 2) / 2
Eg
(7.3 + 7.4) / 2 =
7.35Ω
Relationship between variables
discussed
• I found that the resistance of the wire was
directly proportional to the length.
• With only two exceptions, I found that a
decrease in length of 10 cm resulted in a
decrease of 0.7Ω in resistance
Relationship tested over full range
• The full range was every 10 cm from 100
cm down to 10 cm
• This was 10 sets of information, taken
twice and the average found.
Comments
Comments on the suitability of
procedure
• We repeated the test three times to find
the average results, but we disregarded
the first set of results, as we cut too much
off the wire and we found that the ends
were cut poorly due to a blunt pliers.
• If we were to do this experiment again, we
would ensure three ‘good’ results
Comments on the suitability of
procedure
• If repeating test I would also use thinner
wire, to make it easier to cut.
• I would use sellotape to tie down the wire
to make it easier to read.
Real Life implication
• Electrical appliances where you want to
give out heat, should have a high
resistance, whereas if you want to conduct
electricity it should have a low resistance.
Relationship between Findings and
Problem Statement
• The longer the wire, the more resistance
there is.