Wave-particle duality of electrons
Thought electrons were particles? Well you'd be wrong. Electrons similar to light experiences wave-particle duality. Electrons can be diffracted.
Diffraction of light is the bending of light as it passes through a narrow gap or around an object. In a similar way electrons can be diffracted as they pass through the narrow gaps inbetween graphite atoms.
The electron gun creates a beam of electrons which pass through the thin film of graphite. This causes the electrons to be diffracted and creates a pattern of rings on the screen.
Equation
The de Broglie equation provides a further link between wave and particle
nature and allows the wavelength of electrons to be calculated.
Where mv = momentum (Kgms-1)
Note:
mv is Mass x Velocity and is also referred to as momentum. However as
particles begins to approach the speed of light this equation no longer
applies and thus is sometimes replaced with:
Where p = momentum
In fact all objects, regardless of whether they're as small as an electron
or as large as a football, experience some diffraction, so you're football
is diffracted as it goes through the goal posts! However a large object
doesn't show visible or measurable diffraction because the wavelength
of electrons is so small.