Experimental Methods and Physics Skills /Astrophysical Skills and Techniques Physics and Astrophysics Laboratory Physics and Astrophysics Laboratory Tutors:

Experimental Methods and Physics Skills /Astrophysical Skills and Techniques

Physics and Astrophysics Laboratory

Tutors:

Dr.A.Mahendrasingam (Singam) [email protected]

Professor Rob Jeffries

[email protected]

Physics/Astrophysics Laboratory

Lecture Course Provide an education in the knowledge

required to become a Physicist/Astrophysicist

Laboratory Skills Educating students in some of the skills

required to be a Physicist/Astrophysicist


Module Structure: Two strands

Practical abilities to perform experiments and the intellectual ability to analyse and access the results of experiments (strand 1)

Basic computational skills (strand 2)


The experimental Methods Strand Expected to perform 8 laboratory experiments

during the two semesters ( 5 in semester one, 3 in semester 2)

Your laboratory diary will be marked at the end of each laboratory session. From this mark you will receive a final mark for each completed experiments

Each of these 8 experiments should take you 2 weeks ( 2 x 3 hour laboratory sessions)


The Computing Strand

Spreadsheets Programming


Assessment

Semester one Strand 1 ( 90 marks) Strand 2 ( 10 marks)

Semester two Strand 1 ( 90 marks) Strand 2 ( 10 marks)


Semester oneExperimental StrandBench work Mark(Lab diary for 5 completed experiments) 30

Report 1 30Report 2 30

Computing StrandSpreadsheet exercises associated with any twoExperiments 10

Total 100


Requirement to pass the Laboratory 40 marks out of 100 available ( i.e. 40%)

Submit 4 (2 reports/semester) satisfactory laboratory reports for strand 1

Laboratory contributes 20% to each lecture modules.


Semester 1 Laboratory – Contribution to the Lecture ModulesPHY-10022 20%PHY-10024 20%

Semester 2 Laboratory – Contribution to the Lecture ModulesPHY-10020 20%PHY-10021/23 20%

Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 7 Week 8 Week 9 Week 10 Week 11 Week 12

Report #1Deadline 4.00 PM 21/11/14

Experiments B - M

Experimenton (A) SimpleHarmonicMotion / DataAnalysisandProcessing9/10/14 – 23/10/14

Maths test2-3pm

Lab3-5pm

Lab3-5pm

Laboratory Class (Thursday 14:00 – 17:00)

Maths test2-3pm

Introduction to Laboratory Class – Friday (3/10/14) 10:00 – 11:00 in LJ 1.75

First lab session (Lecture on error and Data Analysis) – Thursday (9/10/14) 14:00 – 15:00 in CBA 1.099/100

First lab session (Worksheet on error and Data Analysis) – Thursday (9/10/14) 15:00 – 17:00 in CBA 1.099/100


Hardback notebook

Your copy of the Lab. Manual

Additional information about the laboratory can be found in the module pages for PHY-10022/PHY-10024 on KLE(http://students.keele.ac.uk)

Laboratory Notebook – Section Front of your notebook should contain:

Name:

Address: School of Physical and Geographical Sciences

Each new experiment should start on a new page

Title of the experiment should be recorded at the start of the each new experiment.

Date should be recorded at the beginning of each laboratory session

Results should be recorded with a short sentence which is sufficiently explanatory that you or someone else can understand it

Record all your data/measurements as you take them

Laboratory NotebookAlways record the units of your measurements along with the measurements themselves

If your data is taken for a certain period of time or a certain number of oscillations etc. then always record this fact along with the measurements themselves.

If you plot or fit your data using one of the computer programs, make a printout of the program output (usually a graph) and attach (glue, sellotape, staple) it into your notebook.

If you use the spreadsheet to analyse the data, make a printout of the spreadsheet and attach (glue, sellotape, staple) it into your notebook.

Laboratory NotebookIf you decide that a set of measurements is incorrect for some reason don’t obliterate it in your notebook. Instead simply draw one diagonal line through it and make a note why you have discarded it. If at a later date you change your mind (or if a staff supervisor or post-graduate demonstrator persuades you to change your mind) you won’t have to re-take the data again. As long as it can still be read it can be used.

Make a note of the pieces of apparatus that you are using in your experiment, e.g. radioactive source B, A.C. circuit box G, a Farnell oscilloscope serial number F831GBX etc. If for some reason a piece of your apparatus is removed (it shouldn’t be but !) then we can recover it if we know the number and you can continue your experiment without having to start again.

At the end of your experiment you should summarise your results, tabulating clearly the values you have obtained for any derived quantities (and their error bars) with suitable notes explaining what each is.

Further details can be found in section 2.1 of the laboratory manual.

PC Lab (LJ1.27) You should able to logon to the computers in the PC Lab using your university computer userid and password.

Also make sure that you save all your work on your network drive (S:).

The networked laser printer in the PC Lab can be used to print your work in the laboratory. Initially you will be given a free 50 pages print quota. Additional print quota can be purchased from Phil.

A key is required to gain access to PC lab. You can obtain a key from Phil by paying a refundable deposit.

You can also use the PCs in the PC Lab in LJ0.026 (Faculty Computing Lab) using Keele Card.

SAFETYBRIEFING FORPHYSICS/ASTROPHYSICS

STUDENTS

Safety

General safety policy

Emergency procedures

Dos and Don'ts

General Safety Policy

The School of Physical and Geographical Sciences must

Provide safe experiments in a safe environment

Establish emergency procedures

Provide safety information and guidance

It is your responsibility to

Take reasonable care for your own health and safety

Take reasonable care for others’ health and safety by complying with the safety rules in the Lennard-Jones Laboratories

Emergency Procedures – FIRE ALARM

THE FIRE ALARM IS A CONTINUOUSLY SOUNDING SIREN

The entire building MUST be evacuated if the siren sounds

Leave either through the foyer or go right along the corridor and leave through the rear building

DO NOT PANICDO NOT TAKE ANY PERSONAL RISKSDO NOT USE THE SERVICE LIFT if the fire alarm sounds

Assemble on the grassed area outside the front entrance of the Lennard-Jones Laboratories

re-entry to the building will not be allowed until Senior Fire Brigade Officer gives permission to do so

Smoke or drink in the laboratory

Drink the water from taps in the Laboratory – There are Drinking Water taps in the toilets

Bring visitors into the laboratories AT ANY TIME

Put bags or coats on the tables

Remove the covers of any equipment or plugs, or use equipment with broken or damaged mains leads

Work in the laboratory without supervision by staff

YOU MUST NOT DO THESE

Store your bag/coats under the bench

Report any suspected faults in equipment to the laboratory staff

YOU MUST DO THESE

Error Bars and the Scientific Process(Lab Manual Section 2.2)

Aim of Science? Advancement of knowledge, understanding nature, etc….

How is this achieved? Building theories/models and testing them by

experimental measurements.

Explaining the results of experiments by theoreticalmodels.

Comparing with theory/other experiments is clearly vital to the scientific process – but how to do this objectively?

Error Bars and the Scientific Process

An error bar X signifies our “confidence” in a value that we measure

X± X

“true” X lies within X- X to X + X ~66%“true” X lies within X- 2X to X + 2X ~95%“true” X lies within X- 3X to X + 3X ~99%



Comparing two values

Experiment and theory (X± X) and (Y)Experiment and Experiment (X± X) and (Y± Y)

Does the value of X lie within the range of (Y± Y)or

Does the value of Y lie within the range of (X± X)

If YES then X agrees with Y within the limits of error or vice versa


Examples

1. The SHM experiment – asked to compare the value of spring constant k measured from Hooke’s law with value measured from oscillations (SHM)

2. -particle experiment – asked to compare measured value of E (determined from R via Feathers equation) with theoretical value of 2.26MeV

Systematic and Random Errors

Broad classification of errors into one of two classes systematic and random

Systematic errors are the same every time you make a measurement.

Random errors “fluctuate” every time you make a measurement

Systematic Errors Zero offset errors in equipment

Limits of measuring scales (e.g. Graduation on ruler/clock in SHM experiment)

How to deal with systematic errors?

Careful calibration, re-calibration of equipment.

Use another piece of equipment to double check.

Reduce scale graduation errors by measuring a larger value. e.g. In SHM experiment measure 10 oscillations instead of one, scale limit on clock is 1 sec whether measure 1 oscillation or 10.

Use the graduation as error bar (sets limit to knowledge) or estimate of offset value (whichever is bigger).

Random Errors

The measured values fluctuate about a true value due to some random process, e.g.

In -particle experiment the count rate varies due to nuclear fluctuations.

In electrical circuit “noise” can lead to fluctuations in measured voltages.

In SHM experiment starting/stopping clock could be different each time you measure 10 oscillations.

The effect of random errors can be treated statistically.

Random Errors

Measure N values x1, x2, x3,.....,xN

• Mean value

N

iix

Nx

1

1

• Standard deviation for the fluctuations

2

1

)(1

1

xxN

N

ii

• The error in the meanN

x

Combining and Propagating Error Bars We have measured a quantity in an experiment, and

worked out its error bar ( call this raw data)

Now we wish to process the value, i.e. use it in a formula.

Since the raw value has an error bar, so must the “outcome” from the formula.

Example, in SHM experiment you measure T, the periodic time and can get an error bar but what you need are values of T2, what is the error in T2

Even worse!!, in the -particle experiment you measure the count rate for thickness of Al, get an error bar in each value and then you need the logarithm of the count rate. What is the error in the logarithm???

The propagation of Errors Through Functions

( ) ( )

( ) ( )

sin( ) sin( ) cos( )

cos( ) cos( ) sin( )

log ( ) log ( )

log ( ) log ( )log ( )

exp( ) exp( ) exp( )

log ( )( )

X X X X X

X X X X X

X X X X X

X X X X X

X X XX

X

X X X XX

X X X X X

XX X X X

2 2

1

10 10

2

10

10 10 10 10

n n n

e e

e

e

n

Combing Errors

Z X Y

Z X Y 2 2Z X Y

Z X Y 2 2

Z X Y Z

Z

X

X

Y

Y

2 2

Z X Y Z

Z

X

X

Y

Y

2 2

ZXY

UV Z

Z =

X

X +

Y

Y +

U

U +

V

V

2 2 2 2

2rA Example

rrA 2

2

2

r

rr

A

A

r

r

A

A

2

Fractional error in A = 2 x Fractional error in ror

% error in A = 2 x % error in r

In general

nrA r

rn

A

A

Fractional error in A = n x Fractional error in ror

% error in A = n x % error in r

Example

What is the value for A?A= x 10 x 10 = 314.16m2

Fractional error in r =0.1/10Fractional error in A =2x0.1/10 =0.02i.e. A/A = 0.02x 0.02 = 314.16 x 0.02 =6.28m2

2rA

mr 1.00.10

26314 mA

Error Bars and Slopes/Intercepts From Graphs

Plot a graph of raw data points, each one has an error bar.

Want to fit a straight line, get slope, use slope in formula.

Since the data points have error bar so the slope of the straight line will also have an error bar.

“Theory” is called least squares data analysis.

DON’T PANIC, leave the theory later.

Computer program on PC’s in lab to fit straight lines and work out error bars. (LineFit / Excel / KyPlot / DataStudio)

Templates for Excel or Kyplot is available on the web in the Physics/Astrophysics Laboratory web page.

Experimental Methods and Physics Skills /Astrophysical Skills and Techniques Physics and Astrophysics Laboratory Physics and Astrophysics Laboratory Tutors:

Documents

laboratory experiments

laboratory diary

laboratory contribution

laboratory sessionresults

lecture modulesphy

lab session lecture

experiments b

results of experiments