soap bubble interference, radioactivity, alpha, betta, gamma radiation, cloud chamber

2. A soap bubble or film is a thin layer of water stabilized by detergent molecules http://www.funsci.com/fun3_en/exper2/exper2.htm Water: speed of light slower Air: speed of light fast Air Incident light will reflect and pass through interfaces. Reflections off the top surface and bottom surface will interfere with each other KEY POINT: 180 degree phase shift when reflecting off interface going from fast to slow (top interface in this case) Detergent layer

3. 180 degree phase shift explains the black color in the thinnest part of the soap film http://www.funsci.com/fun3_en/exper2/exper2.htm Water: speed of light slower Air: speed of light fast Air When film is very thin, path length difference is negligible. So interference is destructive . Appears black because I used black mug. As film gets thicker, there is some path length difference, so interference is not completely destructive – white color. Wikipedia.org Detergent layer

4. Rachelle Regan

6. If we were to learn and apply the mathematical physics, we could very well predict the pattern of colors! You know which colors are missing / present (e.g. magenta = blue + red) It is a really nice way to apply your knowledge of physics!

12. OK, one more thing about charge Charged particles move in curved paths when in a magnetic field Neutral particles move in straight paths Path of a charged particle “ B” is magnetic field

13. Summary of charge characteristics Particles in the universe can have positive (+), negative (-) or neutral (zero) charge Opposite charges attract each other Same charges repel each other “ is proportional to” Charge is conserved Charge is quantized (+1, +2, etc. -1, -2, etc.) Charged particles move in curved paths when in a magnetic field Neutral particles move in straight paths Path of a charged particle Force  Charge1 * Charge2 distance 2

16. X-rays discovered in 1895, Wilhelm Röntgen Cathode Ray Tube (CRT) Röntgen noticed fluorescence across the room (through books and papers) While experimenting with putting objects in the unknown beam, he saw images of his (wife’s) bones appear!

17. Shortly thereafter, radioactivity discovered by Henri Becquerel (1896) (1903 Nobel prize with the Curies) Uranium Salt Photographic film Expose to sunlight Cloudy day / Dark drawer for a couple days Much, much larger effect! The uranium itself was emitting radiation! This sparked the exciting age of nuclear physics, led by Rutherford

20. Three kinds of radiation emitted via radioactive decay named before they were understood…alpha, beta, gamma Alpha particles stopped by paper alpha particles are helium nuclei Beta particles stopped by aluminum beta particles are electrons (or positrons) Gamma rays stopped by lead gamma rays are high energy photons x-rays similar, but lower energy than gamma

23. Alpha, beta and gamma radiation also distinguished by charge behavior Alpha particles deflected by magnet Gamma rays unperturbed by magnet Beta particles deflected opposite alpha It was noticed early on that beta particles behaved exactly like cathode rays (electrons) Alpha particles were discovered to be helium nuclei Gamma rays were very high energy x-rays (photons)

24. Explanation of Geiger counter Depending on the design: Maybe detect alpha-radiation CAN detect beta-radiation Maybe detect gamma-radiation Alpha particles difficulty passing through window But can make it through mica Ionizing radiation (beta, gamma, some alpha) enter through window and create ions inside. These events are detected via the electric current and turned into audible “clicks.”

25. OK, Let’s try to reinforce some learning about alpha, beta, gamma radiation http://www.youtube.com/watch?v=NP9Woxbkr_M

26. The “Inverse-Square Law” First, an introduction to the concept using bread and a butter gun http://www.youtube.com/watch?v=JW3tT0L2gpc

27. The intensity of radiation follows the inverse square law Force  Charge1 * Charge2 distance 2 Intensity of radiation  Source intensity distance 2 Remember for electric charge: If you double the distance, Intensity decreases by a factor of 4