Fysikexperiment i forskning och samhälle, HT 2013

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Gwendoline Hudson
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1 Fysikexperiment i forskning och samhälle, HT 2013

2 What defines physics? What defines a physics experiment? Consider and discuss in groups the two questions above. Define a couple of points as answers to the questions.

3 The teachers answers What characterises physics? Striving for understanding and formulating the principal laws of nature Understanding the physical entities relevant for a physical system Understanding the nature of and interactions between these entities

4 The teachers answers What characterises a physics experiment? Control over cause action Controlled conditions: Control of as many parameters as possible systematic change of parameters Idealisation / Abstraction Reproducibility Fundament in theory and/or model Deliberate perturbation of a system in order to determine the system s characteristics. Make the cause-study the action

5 Boxes Think of physics experiments that could deliver information about the box and its contents. Which physical property would you like to determine? How would you determine this physical property? Why does your measurement allow measuring this particular physical property? What is the length scale of the physical property? What is the length scale of your experiment?

6 Boxes Your measurement method Physical property Probe Measured quantity Length scales of physical properties and measurements mm µm nm pm fm <fm

7 Rutherford scattering

8 Rutherford scattering vs Characteristics of physics experiments Characteristics of a physics experiment Control over cause action Controlled conditions: Control of as many parameters as possible systematic change of parameters Idealisation / Abstraction Reproducibility Fundament in theory and/or model Deliberate perturbation of a system in order to determine the system s characteristics To what extent do these apply to the Rutherford scattering experiment?

9 Probes In Out Out In

10 Probes In Out Photons / Electromagnetic fields Electrons Atoms Ions Neutrons Protons Positrons Antiprotons Muons Pions Neutrinos...

11 Choice of probe Characterisation of a piece of matter: which properties are you interested in? Determination of the properties: disturb by suitabe radiation Choose wavelength according to probed interaction Penetrate into (or emit from) interior or surface only? If you want to receive information on length scales: de Broglie wavelength λ = h/p of same order as (or smaller than) the structure studied Smaller structures higher momentum bigger machines

12 de Broglie wavelengths Wave- length P=E k if photon E k if electr. E k if p/n 10-9 m 1.2keV/c 1.4eV Thermal (10-10 m) (12keV/c) (140eV) m 1.2MeV/c 0.79MeV 0.76keV m 1.2GeV/c 1.2GeV 0.59GeV m 1.2TeV/c 1.2TeV 1.2TeV

13 Common concepts in experimental Physics Each group picks a concept from the list below. During the lectures the group identifies how this concept was relevant in the type of experimental studies that was covered in the lecture. You write a small essay about your concept in relation to the experimental physics you learn bout in the lectures. 2 pages written text plus figures. A preliminary writeup is delivered before the two last lectures. It is peer reviewed by your fellow who give feedbacktogether with one teacher. You respond to the criticism by correcting your text and include the two last lectures. Writing is individual, analysing the concept vs study material may be collaborative Concepts other years: Elastic scattering Inelastic scattering Energy levels Conservation rules (energy, momentum, charge..) Timing Excitation Quantal effects crossections

14 Examples of spectroscopic measurements What do the following terms mean? Spectrum Spectroscopy Where have you previously encountered these terms?

15 Examples of spectroscopic measurements Spectrum = lat. apparition, appearance Came into use in the 17th century for describing what is seen when light is shone through a prism

16 Examples of spectroscopic measurements X-ray photoelectron spectroscopy X-ray absorption spectroscopy Time-dependent x-ray photoelectron spectroscopy

17 Examples of spectroscopic measurements Nuclear probe on meteorite, x-rays Gamma energies from 61 Zn 40 Ca + 24 Mg 61 Zn +p+p+n+γ Almost Rutherford

18 Examples of spectroscopic measurements Particle spectroscopy at high energy Early results from LHC (CMS exp) Masses are the quantal states HEP: often P T instead of kinetic energy

19 Writing articles about physics Any text about physics should be properly referenced. You may quote other sources. But remember: Quotes must be marked clearly. You must always provide the reference of the source (even for internet texts!). Only an insignificant fraction of your text may be composed of literal quotes (i.e., no cut and paste ). Enough information should be provided that a reader can repeat the experiment

Lecture 2: Quantum Mechanics and Relativity

Lecture 2: Quantum Mechanics and Relativity Atom Atomic number A Number of protons Z Number of neutrons A-Z Number of electrons Z Charge of electron = charge of proton ~1.6 10-19 C Size of the atom ~10-10