The Experiment & Competition
Determine the camera constant
- measure d1 and d2 for screen
- measure g1 and g2 on wall
- calculate camera constant g1d1=g2d2=?L.
Measure scattering distance gfax.
Calculate dfax= ?L/ gfax, and divide by magnfication M to get ddust.
File report & uncertainty estimate.
The second part of the experiment, where the unknown “fax” (TEM negative at between 150K and 370K magnification) is used as the sample, often requires that the room be quite dark. When the first group manages to locate a diffraction spot from the unknown, it is helpful to call it to the attention of the other teams, so they know what they are looking for. Remember, since d is very small, scattering distance g will be quite large.
Hardware - We use a He-Ne laser with a tiny (say 4 mm diameter) hemispherical diffusing lens mounted on the front, a 5 cm diameter lens with about 1 meter focal length for focussing, alligator clips in rubber corks for specimen holders, and a wall about 7 meters away for projection.
Caution - The wavelength lamda may be replaced by a question mark (?) in the expanded contents frame.