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

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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 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

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.

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

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

Rotation of a beam Cavendish experiment

Rotation of a beam by rolling Thermal expansion x 2r

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

Shadow magnification by a point light source

syringe laser Shadow magnicifaction by water drop

Cyclops (Cyclops strenuus) Mosquito larva (Anopheles species) Shadow magnification by water drop

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

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

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

Eddy currents Electro motor Magnet Al plate Iron filings

Eddy currents Top view

Eddy currents Side view

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

Presence of invisible substance: how to show presence of g ases? Speed of sound Breakdown voltage Index of refraction What makes them different from air?

Let’s go to work

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