Name...................................................

The University of Reading Department of Physics
The University of Reading - Department of Physics
Student Supervision
Health and Safety Aspects for Experimental Physics I
Supervisor: Ms. Averil Macdonald
This assessment is valid until 1st January 1999.
This assessment was made on 19th September 1998.
Nature of Work
Laboratory work associated with Foundation Experimental Physics I as described in "Foundation Course Experimental Physics I - Instruction
Manual".
Hazards
Electrical Equipment
Heating Equipment
Agreed precautions, control measures and personal protective equipment required
Precautions as detailed in the instruction manual, "Foundation Year
Experimental Physics I - Instruction Manual".
Safety spectacles will be issued for project 6; these should be returned to the laboratory supervisor at the end of the session.
Risk Category for Supervision
Work may proceed because workers are adequately trained and competent in the procedures involved.
Supervisor Ms Averil Macdonald 29th September 1998
1
This assessment refers only to health and safety aspects of supervision. Students must not work in the laboratory outside the timetabled hours for this module.
Experimental Physics 1 Page 3 Foundation Year

The University of Reading Department of Physics
1 Introduction
1.1
Introduction
1.2
Objectives
1.3
Requirements
1.4 Absence
1.5
Monitoring of Log Books
1.6
Safety
2 Assessment
2.2
Laboratory Log Books
2.3 Competencies
2.4
Assessment
5
5
5
6
6
6
5
8
8
10
10
3 Uncertaincies & Errors
3.1
Uncertaincies in Instrument Readings
3.4
Error Bars on Graphs
3.5 Errors in Gradients
3.6
Systematic Errors
3.7 Error in the Final Value
12
12
12
13
13
13
13
4 Project 1: The Bifilar Suspension
5 Project 2 : g by Pendulum 16
6 Project 3 : Thermistor as a Resistance Thermometer 18
7 Project 4 : Specific Heat Capacity
8 Project 5 : Resistivity of a Metal
9 Project 6 : Stress - Strain for Copper and Rubber
22
24
14
20
This booklet describing the module Experimental Physics I is based on the information available at the time of publication. The University reserves the right at any time to change the contents of this module. As much notice as possible of any alterations will of course be given. Anyone who is uncertain of the up-to-date position should enquire of the
Laboratory Supervisor.
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The University of Reading Department of Physics
This booklet is the manual which accompanies the Part 0
(Foundation Year) module
Foundation Experimental Physics
1. The contents of this booklet provide the background for developing skills in experimental physics and specific instructions for the different projects within the module.
This Part 0 (Foundation Year) module is the first of a progressive series of modules offered by the Department of
Physics which are provided to enable you to develop fully the expertise and experience necessary to conduct practical work in physics. This foundation module sets out to:-
(a) show how physicists approach the execution of experiments in order to test, quantitatively, theories and models;
(b) develop the skills in observation and data acquisition and the subsequent analysis required to make such quantitative assessments;
(c) provide practical experience in a range of fundamental physics topics.
You will complete one skills session at the beginning of the module and five experimental projects during the course of this module. All students will be required to keep a detailed experimental log book throughout the duration of this module.
Typically you will work alone and all the assessment will be made on an individual basis.
You will sign up for your chosen project one week in advance to ensure that the appropriate apparatus is available to you and to enable you to undertake the required preparatory work. This will include background reading and producing written answers to associated questions.
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You are expected to complete the experimental aspects of the project and to plot all graphs and undertake any analysis during the laboratory session. If you do not complete the analysis stage of the project during the laboratory session then it must be completed in your own time along with the abstract. Each project should typically involve four to six hours of work, including preparatory work.
If you are absent from a laboratory session you will be awarded a zero mark for that session unless you are able to show that you were ill or involved in an activity for which you have obtained prior approval. You also risk not having lab notes on which to base your formal, assessed write-up (see Assessment). If you are unable to attend the laboratory session you should leave a message on extension
8543 (0118 931 8543) or e-mail a.m.macdonald@reading.ac.uk.
prior to the session.
Your log book must be signed by one of the Experimental Physics
Team at the beginning of the session to ensure that you have undertaken sufficient preparatory
Experimental Physics 1 Page 6
Department of Physics work to begin the project. When you leave the laboratory session you should also ensure that one of the Experimental Physics
Team initials your log book. Log books without initials will not be given a mark, although feedback on the project will still be provided. You must leave your log book on the stand in the laboratory by 12.00 noon on the
Monday following the laboratory session. Log books handed in after that time will not be given a mark although feedback on the project will be provided. The log books will be available for collection from 12.00 noon on the following Thursday.
All of the projects and skills sessions in this module take place in a laboratory within the
J.J.Thomson Physical Laboratory
Building and you are expected to act as professional physicists working in a laboratory environment. Therefore:
•
All coats and bags must be left at the designated sites outside the experimental physics areas.
•
Food and drinks must not be brought into the laboratory.
•
Smoking is not allowed in any part of the building.
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•
You must follow the instructions of the Experimental
Physics Team in terms of safe working practice.
•
You are not allowed to work unsupervised and therefore will not normally be allowed into the laboratory outside timetabled hours.
•
For some projects there are additional specific safety procedures and these are listed in the appropriate chapter.
•
Many of the projects make use of electrically operated equipment. If you suspect that the equipment is faulty you should disconnect it from the mains supply and report the fault immediately to one of the
Experimental Physics Team.
•
You should never attempt to repair or modify the equipment.
•
It is important that you have an appreciation of the capabilities of your apparatus before you start an experiment and so avoid overloading any instruments.
Department of Physics
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The University of Reading Department of Physics
Each project involves some background reading prior to the laboratory session in order to ensure that you are fully conversant with the theory behind your chosen project. Each project is prefaced with some questions and it is essential that you record your answers to these in your log book and that a member of the
Experimental Physics Team signs to indicate that you are adequately prepared to commence your chosen project.
Most prior reading is contained within FLAP modules or "Physics"
(International Student Edition) by
H.C.Ohanian published by
W.W.Norton 1989. Copies of the appropriate material are available in the laboratory and in the
Learning Resources Centre.
All scientists keep a laboratory log book in which they record all of the details, results and calculations related to their work.
Such log books are a working document and scientists record
ideas and discussions as well as hard data.
As part of this module you are required to keep an official laboratory log book; subsequent experimental physics modules will require separate laboratory log books. These may be obtained in the Experimental Physics
Laboratory. All of your work must be contained in this log book and, therefore, graphs etc. must be securely fixed into it at appropriate points. Working on loose sheets of paper within the laboratory is not allowed! Your log book is not a formal report but more a ‘running commentary and should be sufficiently detailed for another physicist to follow your work. It may contain mistakes.
These should be clearly crossed out and a note added to explain what went wrong. At the end of each project you will write an abstract of the project. The following notes should give you a clear idea of the appropriate format and detail. If you are in any doubt as to what is required please consult one of the
Experimental Physics Team.
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2.2.1 What to record in your log book
(a) Each project should start on a fresh page with a title and the date; all text must be written in ink.
(b) All answers to questions undertaken as part of your preparatory work should be included as an introduction to your written work.
(c) You do not need to copy information from this manual but you may need to refer to the diagrams and methods described in it.
(d) Include any diagrams to show exactly how you set up the experiment if they are not already in the manual. In a few cases
(e.g. circuit diagrams) it may be helpful to reproduce the diagram already in the manual as part of your notes.
(e) Results must be tabulated
(where appropriate), must be on a separate page for clarity and must include the appropriate units and estimates of the uncertaincy in your readings.
(f) You should aim to make all calculations and plot all graphs during the laboratory session.
When plotting graphs choose sensible scales, maximise use of the paper and include error bars.
Experimental Physics 1 Page 9
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Make sure that the axes are properly labelled and include a legend to describe the graph.
(g) Quantitative estimates of the errors are extremely important
(see Chapter 3) and must therefore be included at each stage of the calculation.
2.2.2. The Conclusion
Your conclusion paragraph must include an evaluation of your findings including proximity of your value to the accepted value, reasons for any difference and the impact of systematic errors compared with random errors.
You should include a description of the experimental precautions taken and the difficulties, if any, encountered and how you overcame them. Comment on the effectiveness of the technique and the validity of the result. Any suggestions for improving the techniques used should also be included.
2.2.3 The Abstract
The abstract should follow the entry you have made on the particular project. It is to be written with care and should extend to no more than 200 words. The precise format will vary from one project to another but will include:
(a) a brief statement of the objectives of the project in your
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The University of Reading own words. You should not give detail copied from the manual or a textbook.
(b) a short summary of the experimental technique(s) used together with a clear statement of key results along with your estimate of the final error involved
(details of the error calculation should be in your laboratory notes, not the abstract).
(c) a brief conclusion
(d) a comparison of your findings with the literature and brief comments about anomalous or inconsistent results and any systematic errors.
This summary shows what you have learnt from the project and also gives you experience in preparing concise and informative reports.
Remember at all times to think about the physical significance of what you are doing and of any numbers you calculate.
Your progress in developing experimental skills will be monitored via the competency sheet (attached permanently to your laboratory log book) which will give you direct feedback on your strengths and weaknesses.
The competency sheet identifies key skills that are addressed by the projects. Not all competencies
Experimental Physics 1
Department of Physics are appropriate to every project but, by the end of the course, you will have been tested on all of the competencies.
This module is assessed by continuous assessment. Within one week of each laboratory session you will hand in your experimental laboratory log book.
The log book will be examined by one of the Experimental Physics
Team who will provide you with personal feedback on:
•
the quality of your preparatory work;
•
your approach to and operation of the project;
•
the analysis of and conclusions you draw from the results obtained;
•
the analysis of errors and your evaluation of the project in terms of the effectiveness of the procedure and validity of the results;
•
your communication skills as demonstrated in your abstract.
Feedback will be in the form of specific comments on your work together with a more formal assessment of the competencies demonstrated via your competency sheet. This will enable you to identify those skills in experimental physics which
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2.4.1 Weightings
Your marks will collectively contribute to the overall assessment for this module. In addition you will be asked to produce a formal write-up of a specified project (which may be word processed) and you will be interviewed to discuss all of the remaining four projects you will have completed - the viva.
The weightings for the assessment are as follows:
Preparatory Work
10%
Log Book Including Errors
20%
Abstract
10%
Competencies
20%
Formal write-up
20%
Viva (formal interview)
20%
Department of Physics
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readings is not due to the sensitivity of the Errors are not mistakes and should not be covered up or ignored! Indeed the analysis of errors is an essential part of your written evaluation of the project undertaken. Errors are always estimates of the likely or probable departure from some true value.
There is always some uncertaincy in any reading taken as part of an experiment. The uncertaincy in any instrument reading is due to the sensitivity of the scale of the meter used. Typically the uncertaincy is half the smallest scale division readable (or half the last decimal place on a digital meter). The uncertaincy in any instrument reading must be quoted as part of the results table heading.
instrument used (as with the uncertaincies above) but rather due to random (or stochastic) effects. A sensible estimate of the random error in an individual reading can be obtained from the spread of the readings obtained, compared with the average value calculated. Typically 2/3 of the average spread is a reasonable estimate for the random error in a mean value.
(More accurate methods of dealing with errors in mean values will be introduced in
Foundation Experimental Physics
2)
AlI errors can be quoted in absolute terms (with associated units) or as a percentage of the
If you repeat a reading n times, for instance when timing an event, you will probably have n different readings from which you will calculate the average (mean).
The error in individual readings or the mean of such a set of reading. Percentage errors are particularly useful when considering the error in a value which has been derived from some other value(s) e.g. the volume of a sphere. The error here would be due to the uncertaincy in the reading of the radius, r . The percentage error in
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3x the percentage error in r
(because r is cubed in calculating the volume) and must be quoted as such.
N.B. Percentage errors are also used in calculating the total error in a quantity derived from a number of independent values but this will be dealt with in
Foundation Experimental Physics
2).
Every reading plotted on a graph has an error and this must be represented by appropriate error bars. Any line drawn through the points should pass through the imaginary boxes created by ALL of the error bars. Any anomalous points should be indicated on the graph but not included in the best fit line drawn
The error bars on a graph indicate that there is a best fit and two ‘limiting fit’ lines (worst fit) to be drawn. All lines must be drawn and, if appropriate, the best and worst values of the gradient and/or intercept must be calculated.
N.B. a limiting (worst) fit line should also pass through all of the error bars - but only just!
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Some errors cannot be accounted for in the ways detailed above. They are inherent in the system and unrelated to the techniques used and are thus known as systematic errors.
Typical examples would be an incorrectly calibrated instrument, a zero error or poor experimental technique such as parallax error.
Your written conclusion must include an evaluation of the validity of your findings, including the contribution made by any errors involved, both the random errors calculated and any possible systematic errors. You should also comment on how these errors might account for any anomalous results.
N.B. Often one large error will dominate the final result and every effort should be made to identify the dominant errors and time should be spent on reducing them.
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Please complete the answers to these questions in your laboratory log book in advance of undertaking the experimental part of this project.
1. What are the sources of error when timing a pendulum?
2. What procedures is it pertinent to operate to ensure that your value for the timeperiod is as accurate as possible?
3. How does one arrive at the best estimate for the error when measuring the timeperiod?
4. Given the equation below, determine which values should be plotted on a graph to generate a straight line. How will the constant k be derived from your graph?
Procedure:
Set up the apparatus as shown in fig 1. The suspending threads should be parallel and the 50 cm rule horizontal.
Make the distance l = 30 cm and the distance a = 10 cm.
Start the 50 cm rule moving in a twisting motion as indicated by the arrows on the diagram. Measure the timeperiod, T, for the oscillations.
Vary the distance a over a reasonable range and collect a set of measurements of T for your chosen values of a .
Theory predicts that the time period is related to the value a by the equation:
Ref: FLAP P1.1, P1.3,
Objectives:
This experiment will test your ability to manipulate apparatus, to collect and process data and to present your results and conclusions clearly.
Experimental Physics 1 where k is a constant and g is the acceleration due to gravity
Draw a straight line graph which will enable you to verify this relationship and determine a value for the constant k , its units and the percentage error in your value.
Product:
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In addition to the notes, observations, analysis and conclusion produced in your log book while in the laboratory you should review critically the experimental technique you used, commenting on any difficulties you encountered and precautions you took and make any suggestions for ways in which you could improve the accuracy of your results.
Department of Physics
HINT: Was it easy to set up the apparatus as required and to make it twist satisfactorily? Do you consider timing multiple swings and repeating the timing of the pendulum to be worthwhile in improving accuracy? What do you consider to have been the most difficult aspect of completing this project?
Finally write an abstract.
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Ohanian p 171 - 174
Please complete the answers to these questions in your laboratory log book in advance of undertaking the experimental part of this project.
1. As an ideal simple pendulum swings gently back and forth it has both gravitational potential energy and kinetic energy . Define these terms and explain (using a diagram) how the relative proportions vary over one cycle but how the system still obeys the
Law of Conservation of
Mechanical Energy.
Objectives:
You are to find a value for the magnitude of the acceleration due to gravity ( g ) via a direct measurement technique and also by plotting a graph of data. You will consider the validity of your two answers by evaluating the errors inherent in each technique.
Procedure:
Set up a simple pendulum of length l
0
about 0.70 m. Make direct measurements of the length l
0
and the period T
0
for small oscillations and using the relationship
2. The period of the pendulum’s swing will depend on a number of variables. Using dimensional analysis demonstrate which variables of mass of bob ( m ), length of string ( l ) and acceleration due to gravity ( g ), affect the time period ( T ) of the pendulum and find the final form of the equation.
T
0 \
( l
0
/ )
, determine a value for g from your observations. Estimate the percentage error in your value.
3. Why does the technique of dimensional analysis fail to show that there is a factor of 2
π
in the final equation?
Ref: FLAP P1.1, P2.4,
Without changing the length l
0
, set up a modified simple pendulum (see Fig. 1) by clamping a horizontal rod P a measured distance h below the point of suspension 0. The period T for small oscillations of the modified simple pendulum is given by
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T T
0
−
T )
= π 2
Find the period T for small oscillations. Repeat the procedure for a series of values of h between about 0.10 m and about 0.60 m.
Plot a straight line graph of your results which will enable you to find a further value for g and quote the percentage error in this value.
Product:
In addition to the notes, observations, analysis and
Department of Physics conclusion produced in your log book while in the laboratory, you should compare the two values of g obtained by the two methods and their associated errors and consider the relative merits of the two experimental techniques used.
HINT: What is the point of plotting a straight line graph compared with just plugging numbers into an equation a few times and finding an average?
Finally write an abstract.
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Please complete the answers to these questions in your laboratory log book in advance of undertaking the experimental part of the project.
1. The resistance of a thermistor changes significantly with temperature but in a different way to most metallic conductors.
Describe the difference between metallic conductors and semiconductors in the way they react to changes in temperature.
2. Define the ‘temperature coefficient of resistance’. What is the meaning of NTC and PTC in this context?
3. What are the two fixed points used to calibrate any thermometer on the celsius scale? What does this assume about the behaviour of the material?
4. Draw a circuit diagram of the circuit which will enable you to measure the resistance of the thermistor as it experiences changes in the temperature of its environment. Why is it important
Experimental Physics 1 to keep the current through the device low?
Ref: FLAP P4.1, P7.2, P11.4
Ohanian p498-500, p522-4
Objectives:
You are to calibrate a thermistor as a resistance thermometer on the celsius scale in order that you may use it to determine a value for room temperature. You will investigate resistance as a thermometric property and consider its usefulness compared with more traditional liquid in glass thermometers
Procedure:
Set up a circuit with an ammeter and a voltmeter which enables you to determine the resistance of the thermistor without the current heating it up significantly.
Calibrate the thermistor as a thermometer on the Celsius scale using resistance as the thermometric property.
Determine the resistance of the thermistor at room temperature and hence find the temperature
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Evaluate the errors in your value for room temperature compared with the error inherent in a liquid in glass thermometer
Product:
In addition to the notes, observations, analysis and conclusion produced in your log book while in the laboratory, you should comment on the effectiveness of this technique for measuring temperature and the validity of the answer for room temperature obtained. Any suggestions you have for improving the experimental set up should also be included.
HINT: Is a thermistor more accurate than a liquid in glass thermometer? In what circumstances might you select a thermistor rather than a liquid in glass thermometer?
Finally write an abstract
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Apparatus:
Thermistor
Power Pack
2 Avometers
250 cm beaker
Ice
Heating apparatus:
Bunsen Burner
Tripod
Gauze
Heatproof mat
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Ohanian p516, p628
Please complete the answers to these questions in your laboratory log book in advance of undertaking the experimental part of the project
1. What is the definition of the volt? How would you calculate the total electrical energy delivered to a device?
2. Draw a circuit diagram which will enable you to determine the amount of electrical energy delivered to a heater embedded in a metal block over a fixed time.
Objectives:
A 1kg block of copper is to be heated electrically. You will investigate the effect of heat loss on the maximum temperature achieved and therefore calculate the specific heat capacity of copper. You will consider how corrections to results are made and consider the validity of such
.
corrections.
Procedure:
Set up the circuit and incorporate a variable resistor so that the voltmeter needle can be set to an appropriate reading.
3. It has been discovered that aluminium has a specific heat capacity of 910 J/kg/K. What is meant by the term ‘specific heat capacity’? What is meant by the word ‘specific’ in this context?
Deliver a fixed amount of electrical energy to the block and record the subsequent rise in temperature.
4. If an unlagged object is heated it loses heat to its surroundings.
A ‘cooling correction’ can be calculated to account for the heat lost by plotting a cooling curve.
Explain how a cooling correction is calculated.
The block is not lagged so a cooling curve has to be drawn to enable you to determine the maximum achievable temperature.
Calculate the specific heat capacity of copper for the values
Ref: FLAP P4.1 P7.4,
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The University of Reading obtained and evaluate the errors in your value.
Product:
In addition to the notes, observations, analysis and conclusion produced in your log book while in the laboratory, you should comment on the effectiveness of this technique for determining the specific heat capacity of a metal and the validity of the answer obtained.
Any suggestions you have for improving the experimental set up should also be included.
HINT: Is all the heat energy supplied to the heater transferred to the block? Is it reasonable to take the temperature indicated on the thermometer as valid for the whole of the aluminium block? Is heat lost at a constant rate from an unlagged block?
Finally write an abstract
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Power Pack
Voltmeter
Digital Multimeter
Copper block & heater
Thermometer -10 - 110 C
Stop Watch
15 ohm rheostat
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Please complete the answers to these questions in your laboratory log book in advance of undertaking the experimental part of the project
1. All materials exhibit a resistance to the flow of electrical current. Describe how this resistance arises within a metal.
2. Define the ‘resistivity’ of a metal. What are the units of resistivity? By dimensional analysis find the fundamental units from which the unit of resistivity is derived.
3. Draw a circuit diagram to enable you to measure the resistance of a wire as you vary the length of the wire.
4. How can you ensure that you do not draw a current of more than 1A at any time? Why is it important not to draw a high current?
Ref: FLAP P1.1, P4.1
Ohanian p 685 - 7
Experimental Physics 1
Objectives:
You will create and operate an electrical circuit which will enable you to evaluate the resistivity of a metal wire. You will compare and contrast digital and analogue meters for use in electrical circuits.
Procedure:
Set up a circuit using an ammeter and a voltmeter to enable you to determine the resistance of the total length of the wire 1.5 m.
Vary the length of the wire but do not exceed a current of 1A.
Plot a straight line graph and hence find the resistivity of the metal. Evaluate the error in your value.
Product:
In addition to the notes, observations, analysis and conclusion produced in your log book while in the laboratory, you should comment on the effectiveness of this technique for determining the resistivity of
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HINT: Why is it good experimental practice to repeat the readings for increasing lengths of wire as well as decreasing lengths? Why should the diameter of the wire be measured at various points along its length and at various orientations? Do analogue meters have any advantage over digital meters for an experimental set up such as this? In what circumstances would an analogue meter be preferable to a digital meter? In what circumstances are digital meters preferable to analogue meters?
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Apparatus:
1.5m Resistance Wire
[constantan or nichrome].
Digital Voltmeter
Avometer
Power Pack
Micrometer
Metre Rule
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Please complete the answers to these questions in your laboratory log book in advance of undertaking the experimental part of the project
1. The Young’s Modulus for a material is defined as the ratio of tensile stress to tensile strain.
Define the terms ‘tensile stress’ and ‘tensile strain’ and describe a material’s behaviour if it has a high value of Young’s Modulus.
You are to investigate the behaviour of copper under tensile stress and measure its breaking stress. You will then compare its behaviour with rubber, a material more commonly described as elastic to see how different it is.
Both experiments require ingenuity in setting up to make best us of the available apparatus.
2. What are the units for Stress,
Strain and Young’s Modulus?
3. When stretched metal will reach an ‘elastic limit’ and exhibit
‘plastic flow’. Explain what is meant by these two terms and explain what is happening on a molecular level within a metal when this happens.
Ref: FLAP P7.6
Ohanian p366 - 9
Procedure:
Part 1: Copper.
Set up the apparatus as shown in Figure 1. Load the wire slowly, 200g at a time, marking the position of the pointer on the graph paper.
Continue loading the wire until it breaks. Discard the wire after use.
N.B. At times of plastic flow the pointer may turn by more than one complete rotation. This must be noted.
Objectives:
Represent the behaviour of the copper wire graphically and use your readings to generate a value for the Young’s Modulus
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Part 2: Rubber.
Devise a means by which an elastic band may be hung and loaded and its extension measured. Measure the extension of the band over a number of cycles of loading and unloading.
Represent the behaviour of the rubber graphically
Product:
In addition to the notes, observations, analysis and conclusion produced in your log book while in the laboratory, you should comment on the effectiveness of your techniques for determining the Young’s
Modulus of these materials and the validity of the answers obtained. Any suggestions you
Department of Physics experimental set up should also be included.
HINT: Consider the difference between the materials on a molecular level when comparing their different responses to stress. Does the rubber exhibit hysteresis when loaded and unloaded repeatedly?
Apparatus:
2m Copper Wire
Pulley to clamp to bench
Straw and graph paper
G - clamp and wooden blocks
Hanger and weights
Micrometer
Thin Rubber Band
Clamp Stand
Half Meter and Metre Rule
Safety Specs have for improving the
Experimental Physics 1
Anything else
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