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Makeing invisible visible

Makeing invisible visible. Gorazd Planinšič Faculty fot Mathematics and Physics, University of Ljubljana, Slovenia. Experiment should convince. Outcomes of experiments should be as evident as possible even for the student in the last row

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Makeing invisible visible

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  1. Makeing invisible visible Gorazd Planinšič Faculty fot Mathematics and Physics, University of Ljubljana, Slovenia

  2. Experiment should convince • Outcomes of experiments should be as evident as possible even for the student in the last row • All senses (not only sight) should be used to make outcomes of the experiments perceptible and convincing We should also tell students that in practice often huge technological efforts and new scientific knowledge is required to achieve small increase in sensitivity of detectors

  3. Two types of approaches • Observation by magnification (amplification): object or change is too small to be observable. Optical or other methods are used to make the object or change perceptible. • Observation via agent: property of an object or part of a space is invisible or very hard to be seen. The property in question is made visible or amplified indirectly by an agent.

  4. Observation by magnification • Rotation of a beam • Projection • Refraction (angular magnification)

  5. Rotation of a beam R L Large displacement Large radius Small angle

  6. Rotation of a beamCavendish experiment

  7. Rotation of a beam by rollingThermal expansion 2r x

  8. 2r m => cm Rotation of a beam by rollingDeflection of a wall x L D L MacIsaac, M Nordstrand, Demonstrating and measuring the flexure of masonry wall, TPT 41(2003)74.

  9. Shadow magnificationby a point light source

  10. Shadow magnicifactionby water drop syringe laser

  11. Shadow magnificationby water drop

  12. Shadow magnificationby water drop Cyclops (Cyclops strenuus) Mosquito larva(Anopheles species)

  13. Water flea shadows magnification G Planinsic, Water drop projector, Phys. Teach. 39 (2001) 18-21

  14. Observation via agent • Electric and magnetic field: reorientation of small particles (iron filings, salad seeds), oscillations of compass needle... • Gas flow and liquid flow: streamers • Temperature distribution: IR photography, LCD thermometers • Stress distribution: light polarization

  15. Observation via agent • Small vibrations: waves, ripples, bouncing ping-pong balls.. • Presence of gases

  16. Eddy currents Iron filings Al plate Magnet Electro motor

  17. Eddy currents Top view

  18. Eddy currents Side view

  19. Small vibrationsSinging wine glasses G Planinsic, More fun with wine glasses, Phys. Teach. 37 (1999) 33-35.

  20. Presence of invisible substance:how to show presence of gases? • Speed of sound • Breakdown voltage • Index of refraction What makes them different from air?

  21. Let’s go to work

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