Observations and first qualitative results

• In the middle of the screen one sees a bright green spot.
• At distances r₁ and r₂ from this point one sees two less bright rings.
• With increaing acceleration voltage, the distances r₁ and r₂ become smaller.

Electron diffraction

When the electron beam passes through the polycrystaline graphite film, something must occur that produces the two rings to appear on the screen. The designation of the experimental setup as"electron diffraction tube" and recalling a Experiment - in which a laser beam passes through a slit or grating and a so-called interference pattern appears on the screen - provide first clues to what causes the spots.

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