Working with Xplora Knoppix: General introduction and

Working with Xplora Knoppix:

General introduction and practical exercises

on the web experiment “Electron Diffraction”

Assimina KontogeorgiouKarl SarnowXplora

Web experiments are:Real experiments, operated from our desktop, while the experimental apparatus is at a remote location.

Located in real places, where a webcam give us a view of the set up.

Connected to a database. The results of all the experimenters are saved, so a statistically significant number of data points will be accrued, allowing us to see the validity of the result and the influence of random.

Web experiments are:

Maintaned by professionals and therefore run with high availability and reliability.

Bringing the concept of remote – controlled laboratories from today's large multinational research institutions into school laboratories.

As a result

Great tools for science teaching

Practical science procedures controlled at a distance, using a web site.

What are the benefits of web experiments?

Enable teachers to do an experiment in class which is too expensive, dangerous or complex for a normal school laboratory.

Enable a teacher to prepare laboratory sessions that can be carried out by students independently. The results go into the database and are a topic for common analysis in classroom.

Enable teachers to achieve a better level of scientific quality from the combination of the experiment and the database.

What are the benefits of web experiments?

Allow direct comparison of results with that of other users. The statistics of all results enables the experimenter to weigh a bad result in an appropriate way. Hence, there is more value for a bad result than just “bad”.

Do not require experimental set – up time for a teacher and tecnicians.

Web experiments available at XPLORA web site:

The web experiment: Electron diffractionLocated at the URL:

http://www.xplora.org/ww/en/pub/xplora/megalab/web_experiments_examples.htm

Set up by the AG Jodl of the physics department at Kaiserslautern univercity: url: http://pen.physik.unikl.de/w_jodl/

Diffraction: a wave phenomenon

Electrons are charged and interact strongly with matter.

They have corpiscular and wave properties,so we will name them “quantum objects”.

The combination of the old Newtonian corpiscular theory of light with the Huygens wave theory of light was integrated into the Einstein/Planck quantum concept and it is applied for quantum objects.


The prolongation of the quantum concept, from light to matter, comes by De Broglie in 1923.

He stated that particles have wave properties.

In 1927, at Bell's laboratory in USA, C. J. Davidson and L. H. Germer proved that, that electrons have a wavelength

= h/p.λ

G. P Thomson, the son of J.J. Thomson proved the same property at the same time in England.


W.L. Bragg in 1913, found that crystals gave remarcably characteristic patterns of reflected Xradiation.

He presented a simple explanation of the observed angles of the diffracted beams from a crystal,

that it is applied for the electron and any other quantum object beam, too.


The conditions for a sharp peak in the intensity of scattered radiation were:

The incident beam should be specularly reflected by the ions in any one plane.

The reflected rays from succesive planes should interfere constructively.


The path difference between the two rays is equal to an integral number of wavelengths:

n = 2 d sin λ θ

Electron diffraction: The experimental setup

Electron diffraction: The experiment

Electron diffraction: The graphite structure

Graphite has the diamond structure,hence it has two interplanar distances

v = (2eU/m)1/2

Electron diffraction: The equations

sin =R/l Ddθ = λ

n = 2 d sin 2lλ θ

eU = 1/2mv2

v= fλ

E=hf

E=pv

p=mv

=h/m*v λ

Electron diffraction: The experiment and its pedagogic backround

For a student it is really fascinating to discover electron's wave nature.

while, many experiments in the school lab demonstrate the wave nature of light.

Students will be really excited by thinking about the interference of a car at a garden fence, but ...quantum theory is manifested in the microcosm!

Electron diffraction: The experiment and its pedagogic backround

The idea, that matter can interfere seems very strange and this is where the webexperiment hooks in.

Students can mesure the interference of electron at a grid.

The motivation for having this experiment run by them is normaly very high and should not be underestimated as an overall physics booster.

Electron diffraction: The web experiment How to be used

In a real school:

The physics teacher will be happy to have one working diifraction tube.

He/she will not give away the tube for students experiments.

There are too many schools around in Europe, where the teacher can not use a single diffraction tube.

For all these cases the web experiments are created.


The teacher explain the experiment

The teacher explains the measuring procedure, including the procedure for preparing the notes of the experiment.

Each student gets the task to conduct an experiment for one voltage with repetitions in total.

The task should have a time slot of some days depending on the number of pupils.


The student task includes the creation of a report of the experiment, which contain three parts:

The experimental setup.

The experimental procedure.

The description of calculating the results from the experimental data.


Three scenarios are possible:

1. Calculate the wavelength of an 1. Calculate the wavelength of an electron.electron.

This is based on the tube and crystal geometry and acceleration voltage.

Then, the wavelength is compared with its value from the De Broglie equation.


From this calculation the student will get:

A verification of De Broglie concept.

Insight into which of the interplanar distances of the graphite crystal is responsible for a specific interference pattern.


2. Use the wavelength to determine the 2. Use the wavelength to determine the interplanar distance of graphite:interplanar distance of graphite:

If De Broglie's equation has been accepted, the If De Broglie's equation has been accepted, the interplanar destances can be calculated.interplanar destances can be calculated.

3. Determine Planck's constant 3. Determine Planck's constant h,h, from the from the experimental data using experimental data using De Broglie's equationDe Broglie's equation.

This scenario is of minor didactic importance This scenario is of minor didactic importance and reflects more accuracy aspects of the and reflects more accuracy aspects of the experiment.experiment.

Electron diffraction: Tools needed for student lab work

Internet access from home or from the school library.

A graphics software (GIMP)A graphics software (GIMP)

A spreadsheet program (OpenOffice.org Calc, A spreadsheet program (OpenOffice.org Calc, Excel).Excel).

A word processor, which should have a good A word processor, which should have a good formula editor (LyX, OpenOffice.org Writer, formula editor (LyX, OpenOffice.org Writer, Word).Word).

Open Source Software

GIMPGIMP, , OpenOffice.orgOpenOffice.org and LyXLyX are Open Source products.

They are freely distributed by the teacher.

The XPLORA – Knoppix DVD is a complete ready to run solution, which a teacher or a student may freely download, distribute and use from url: www.xplora. org

Electron diffraction: Conducting the experiment

'Click on the icon “web Experiment”.

Click on the web experiment we want to conduct.


'Reserve a time slot.

The selected date and time will be acknowledged by email.


'At the reserved time slot,click on “Conduct the web experiment”

Click on “Launch web experiment”


'Click on “Labor”.

After inserting the data, the click on the button switches the tube on.

Electron diffraction: Analysing a screenshot


Zoom factor: 2 (2:1)

V = 3999 V


V = 4,899 KV

Electron diffraction: Calculate the results

Statistics of the results with OpenOffice.org CalcOpenOffice.org Calc

Experimental calculations for electron diffraction Webexperiment

Ua(kv) D(pixel) D(cm) 1(m)λ 2(m)λ v (m/s) _DeBroglie (m)λ 1Δλ 2Δλ2,5 3,49 3,2215 2,54E011 1,47E011 2,97E+007 2,45E011 3,48% 67,14%2,5 5,76 5,3169 4,19E011 2,42E011 2,97E+007 2,45E011 41,52% 1,27%

0,0000 0,00E+000 0,00E+000 0,00E+000 #DIV/0! #DIV/0! #DIV/0!0,0000 0,00E+000 0,00E+000 0,00E+000 #DIV/0! #DIV/0! #DIV/0!

d/cm 12Calibrationpixels 13

cm/pixel 0,92

v = (2eU/m)1/2 (3)d1=2,13E010 m d2=1,23E010 m

v= *fλE=h*f =h/me*v (2)λE=p*v

D: diameter of diffraction patternd: interplanar spacingl: distance graphite foil – screen

Calculated according equation 1

Calculated according equation 2

=D*d/2*l λ (1)

Electron diffraction: Global Cooperation

Students may see how other students performed conducting the experiment.

It is recommended that students insert their results into XPLORA database.

Even if they are not able to use a spreadsheet program, they can use the output of the database for creating their notes.

Electron diffraction: Input the data into the database

Click on the “Input a Web Experiment result”.

The dialog for the input of data opens.

A table of results is shown.

Entries with unusable data marked red.

Nowadays, internet give us the possibility to carry out web experiments without any difficulty.

Internet is only a part of ICTs.It is obvious that ICTs change the perspective of teaching and learning methods very quickly.

Teachers and students take advantage of them only if they are ready to follow up.

Thank you for your attention!

Documents

Working with Xplora Knoppix: General introduction and