Electrons, travelling at speed 
in a vacuum, are incident on a very thin carbon film, as illustrated in the figure below.
The emergent electrons are incident on a fluorescent screen. A series of concentric rings is observed on the screen.
Suggest why the observed rings provide evidence for the wave nature of particles.
The initial speed of the electrons is increased. State and explain the effect, if any, on the radii of the rings observed on the screen.
A proton and an electron are each accelerated from rest through the same potential difference. Determine the ratio
of the electrons decreases, hence the radii of the rings observed on the screen decrease.
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