Physics 109  Some study topics for the last three weeks.


8 May 2007: Listed here are some study topics which I think deserve your attention for the material since the second test.


  1. Light, cameras, film etc.

Be sure to understand the different ways in which light is produced by the types of bulbs we demonstrated in class. Those include incandescent bulbs (know about black body spectra), gas-discharge lamps which pass a high voltage through a gas tube such as neon or helium, fluorescent bulbs and lasers. The text does a very good job of describing these. Remember that visible light (wavelengths between about 700 nm and 400 nm) is bent in glass or plastic owing to the fact that the speed of light in that material is less than the speed of light in a vacuum.


Remember that film speeds are faster when the grains of silver halide are bigger and thus the pictures grainer. Do large-diameter or small-diameter lenses have better depth of focus? Why?


Remember why light disperses into a rainbow in prisms.


The dual nature of light (photons like particles and waves that interfere) is true of all electromagnetic radiation.  It is also true that particles can exhibit wave-like behavior in their interaction with small objects.  For example, electrons can also generate interference patterns even if only one electron at a time were to interact with a crystal acting in a manner like a double slit or a grating does with visible light.


UV light does not penetrate glass because the photons are sufficiently energetic to cause the photoelectric effect.  Visible photons go through glass without doing that.  But visible photons do set up vibrations of the electrons in glass and that can be thought of as the reason for the speed of light in that glass being less than c.


Shorter wavelengths of light can scatter from smaller objects.  When the wavelength of electromagnetic radiation gets much larger than a given small object there is very little absorption or scattering of the wave by that object. On a similar topic, we need short wavelengths to "see" or probe small objects. Light of wavelength 800nm is not generally able to "see" something , say, 200 nm in size.


All exothermic reactions result from the changing of mass to energy.  This is true for chemical burning and also for nuclear fusion (of lighter nuclei) and fission of heavy nuclei.  The burning, the fission of U-235 and the fusion of H on the sun into He nuclei all result in more tightly bound objects with correspondingly lower mass.


These are some of the new items of the final three weeks. Good luck!!