Laboratório de Electromagnetismo e Ótica · P. Conde Muíño Laboratório EO (MEAer/LEAN) 6...

Laboratório de Electromagnetismo e Ótica

MEAer/LEAN 2020-2021

P. Conde Muíño Laboratório EO (MEAer/LEAN) 2

Presentation

★ Lab professor

➡ Patricia Conde Muíño

Contactos: [email protected]


Planning

★ Objectives:

➡Complement the theoretical lectures with experimental classes about some of the course contents

★ Lab classes

➡6- 9 October: experiment 1, Laws of Ohm and Kirchhoff

➡2-6 November: experiment 2, Magnetic Field

➡30 Nov-4 Dec: experiment 3, Optics (waves)

➡Classes of 5/Out & 1/Dec: to be recovered on 4-8 January

★ In each lab class:

➡Maximum 6 groups

➡3 persons/group


Schedule of the lab weeks

★ New class created

➡Monday 15-17h

★ Please register till the end of today


Lab room: C01

★ Picture when it started to be organised


COVID-19 security rules

★ Use of masc is mandatory in the lab.

➡Should cover nose and mouth all the time

★ It is forbidden to eat/drink at the lab

★ Movement within the lab should be done following the indications

➡Minimize the crossings of people

★ Students should be ready in front of the lab at the time indicated in the schedule

➡ Labs will start 10 min later

➡This time allows entering the room in an organised way



★ Entering the lab:

➡Wait for the instructions of the professor before entering

Suggestion: organized queue with security distancing

➡Desinfect your hands before entering

➡Follow the indications to move

➡Drop you personal belongings on the designated area

➡Take to the lab desk only what you need to the experiment

➡Desinfect the equipment before starting your work



★ During the execution of the experiment

➡Do not move around except if it is strictly necessary

➡Desinfect your hands regularly

➡Keep a safe distance to your colleagues

★ End of the lab:

➡Finish in time

➡Allow enough time to desinfect the equipment and the desk before leaving

★Additionally:

➡Only 2 (out of the three) students per group can be in the lab

The 3rd one attends remotely

Rotation: all the students should attend at least 2 lab classes

➡Registration of the students attending the class


Lab work

★ During the class you should take all the measurements and do the calculations/plots that are possible

★The 3rd student (remote) can contribute to the data analysis and help with ideas/suggestions on how to do the measurements

➡Should be available to speak with the professor during the class

★It is mandatory to deliver the lab report with all the measurements before leaving the class

★Additional calculations, plots and comments can be send by e-mail till the end of the following day

➡Should be a pdf file, only one file

➡Facilitates the remote group member to participate


Before the 1st class

★Organize the groups before comming to the lab

➡Who attend physically the class when?

➡Ensure that the group can enter organized on the first lab

➡Ensure that all group members attend 2 labs physically


Evaluation

★ Lab: 25% of the final course note

➡Minimum of 8.5 points

★ Evaluation criteria:

➡Class preparation: 15%

➡Performance during the execution of the lab: 30%

➡Presentation of tables, graphs and results: 15%

➡Calculations and results obtained 20%

➡Conclusions and critical evaluation: 20%


What you need to know

★ Preparation of the classes: mandatory

➡ Understand the theory: what you need to measure and expected results

➡ How to do the measurments and what you need to do when arriving

➡ Time during the class very tight in some cases

★ Performance during the class

➡ Do the measurements with precision and care

Try to reduze the uncertainties

Ensure that the measurements are as precise as possible

➡ Take all the necessary measurements to have the correct results ➡ Repeat measurements if something is wrong

➡Ask in case of doubt!

➡ Finish all the measurements


What you need to know (II)★Presentation of results

➡ Measurements should always come with an uncertainty ➡ Right number of significative digits ➡ Units

★Calculations and results obtained ➡ Correct fits/derivation of the calculated results ➡ Propagate the uncertainties correctly to derived results

★Conclusions and critical analysis of your results ➡ Describe the conclusions you take from your measurements

If they don’t match your expectations: why? Justify which uncertainties may have lead to your results

➡ Identify possible systematic uncertainties

Quantify as much as possible ➡ Evaluate critically your result taking into account your uncertainties


Organisation of the class

★Work in a team

★Focus on the measurements during the class


Bibliography

★ Available at Fenix:

• Lab guides

• Guide about uncertainty calculation and presentation of results

★ Physics for Scientists and Engineers : R. A. Serway, J. W. Jewett 2004 ISBN: 0-53-440842-7

http://www.brookscole.com/serway


Exactitude versus accuracy

Accuracy: degree of agreement between several measurements

Exactness: how close are the measured numbers to the “truth” or “nominal” value. This distance is called experimental error.


Systematic and random errors

•Bad calibration conditions of measurement instruments•Use of instruments in non-recommended conditions•Systematic incorrect readings of the observer•Using a physical method that is not adequate for the measurement

SYSTEMATIC ERRORSSmaller

exactness

•Lack of sensitivity of the instrument or observer•Randomly wrong readings of the observer•Noise (mechanical or electrical fluctuations or vibrations)•Statistic processes associated to the observed phenomenom (e.g. radioactive decays).

RANDOM ERRORS

Smaller precision

Correction: better calibrations, adequate handling of equipement,…

Lead to systematic uncertainties


Presentation of results

★ Measurements come with their uncertainty plus their units

x ± Δx cm

★Uncertainty from the measurement instruments

➡Digital instruments: the last significative digit

➡Analog instruments: half of the last significative digit

2.6 ± 0.1 V

74.5 ± 0.1 V

Assume scale large box = 1 V


Uncertainty of the mean

1. Large number of measurements

➡Mean value provides the best estimate of the truth value

➡Uncertainty of the mean value = standard deviation

2.Small number of measurements (N


Propagation of uncertaintis

Calculated quantity: F(X,Y;Z) with X, Y,Z being the measurements with uncertainties ΔX, ΔY, ΔZ

Example:


Presentation of results

★Measurements should be presented with uncertainties

➡Uncertainty: one/two significative digits

➡The measured/calculated value should agree in number of significative digits

➡ALL measurements come with UNITS (preferably IS)


Plots and graphs

★Include uncertainty on the measurements

★ Remember:

➡ Identify the x,y lables and include units always


Fitteia

★Web tool relatively easy to use that does fits properly (including uncertainty calculation)

http://fitteia.org/
http://fitteia.org/

Laboratório de Electromagnetismo e Ótica · P. Conde Muíño Laboratório EO (MEAer/LEAN) 6...

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