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 WireSETTING on MultimeterTHICKNESS 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

• 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

Resistance1 / Ώ

Resistance1 / Ώ

Total Resistance1 / Ώ

100 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.