Electron diffraction

[Lizwi]

Does the electron change the direction as it passes through a slit?

[Bufofrog]

The diffraction pattern is due to the electrons being waves and the waves interfering with each other and not due to electron 'particles' changing direction.

[studiot]

1 hour ago, Lizwi said:

Does the electron change the direction as it passes through a slit?

Only waves can diffract.

As noted, diffraction of electrons is a manifestation of the wavelike characteristics of electrons.
 

Changes of direction of an electron considered as a particle is called scattering.
There are various forms of electron scattering.

See here

https://en.wikipedia.org/wiki/Electron_scattering

[Enthalpy]

In case the electron had a rather well defined direction before the slit, it implies that its lateral position wasn't so precise.

A slit narrower than the width of the previous electron's wavefunction (the lateral position) makes the wave narrower if the electron passes through, and then the electron's direction is less defined, so the electron can be detected in a position that was not attainable to it before it passed the slit.

This is described in more details for light and is called "diffraction", so you can read for instance the Wiki articles. Electrons do the same for being waves too.

[swansont]

10 minutes ago, Enthalpy said:

In case the electron had a rather well defined direction before the slit, it implies that its lateral position wasn't so precise.

A slit narrower than the width of the previous electron's wavefunction (the lateral position) makes the wave narrower if the electron passes through, and then the electron's direction is less defined, so the electron can be detected in a position that was not attainable to it before it passed the slit.

This is described in more details for light and is called "diffraction", so you can read for instance the Wiki articles. Electrons do the same for being waves too.

Diffraction depends on the deBroglie wavelength, not the wave function.

The deBroglie wavelength is dependent only on the momentum. Slits do not make this wave narrower.  

 

[Enthalpy]

If the  electron has passed the slit, its wavefunction at the exit is as narrow as the slit.

Edited October 7, 2019 by Enthalpy

[swansont]

3 hours ago, Enthalpy said:

If the  electron has passed the slit, its wavefunction at the exit is as narrow as the slit.

What does that have to do with diffraction?

[Enthalpy]

The narrower wavefunction as exiting the slit allows the electron to be detected in directions that were inaccessible to it when the wavefunction was wider hence more directional before the slit.

[swansont]

41 minutes ago, Enthalpy said:

The narrower wavefunction as exiting the slit allows the electron to be detected in directions that were inaccessible to it when the wavefunction was wider hence more directional before the slit.

That would imply that the effect depends on the spatial extent of the beam. In what equation does this prediction appear?

 

[Enthalpy]

Are you kidding? That's for instance the position-momentum uncertainty.

Or the diffraction limit of a lens, and antenna and so on.

[swansont]

If the wave function is as narrow as the slit, how does two-slit interference occur?

If a barrier redefined a wave function as you describe, how does quantum tunneling happen?

[Enthalpy]

Hey Swansont, I hope you are only conducing tests for some potential employer. What you ask here is not your normal level.

The wave function must be narrow behind each slit in order to spread with the distance so the illumination by the slits overlap in some screen region. Within that overlap region, interferences are observed and prove that the photon passes by both slits.

In this experiment, the obstacle that bears the slits is chosen opaque enough to neglect light passing through. Nor would I model this absorption by an energy barrier, as they are difficult for photons, and because barriers reflect particles instead of reflecting them. And light passing through such an obstacle wouldn't be tunnelling.