Are the electrons in TV set wave or particle?

[feynmann]

The interpretation of Quantum mechanics wavefunction indicates that it can only predict the probability where the electrons might be. So the next positions will be totally random.
But the positions of electrons in TV set seem to be pretty predictable, otherwise the screen won't show a good picture

 

[mgb_phys]

Electrons are particles, but all moving particles behave like waves, with wavelength = h/momentum.

Electrons in a TV are moving fast enough that you have to take into account relativity but the wavelength is still roughly = h/mv.
Since h (Plank's constant) is very small = 6.626 ×10⁻³⁴ Js the wavelength isn't very large and the electron appears as a sharp point.

The fact that the wavelength is so small is why electron microscopes can see much smaller detail than optical ones.

 

[DaveC426913]

But the positions of electrons in TV set seem to be pretty predictable, otherwise the screen won't show a good picture

The position error is microscopic in scale, not macroscopic.

 

[feynmann]

The position error is microscopic in scale, not macroscopic.

Where is the boundary between microscopic and macroscopic?

 

[DaveC426913]

Where is the boundary between microscopic and macroscopic?

There is no boundary; it is a continuum.

All objects, from planets down to electrons are both waves and particles at all times.

Planets behave A LOT like particles (easy to know where they are and how fast they're moving); while their wave properties are jumbled together.

This is the crux of Schrodinger's Cat. In principle an object the size of a cat can be treated as a wave, or can be seen in superposition (just like particles can), but in practice, you're dealing with the wave functions of uncountable particles; they will collapse into one cat.

 

[jtbell]

To make an analogy with light: an unobstructed laser beam follows basically a classical trajectory, but if you put a narrow slit in front of it, you get a diffraction pattern. Looking at the original beam more closely, if you let it propagate a long distance, it spreads because of diffraction at the aperture of the laser.

Similarly, in undergraduate physics labs, a common experiment is to take a narrow beam of electrons (comparable to the ones produced in a CRT), send it through a crystal (lots of narrow "slits") and observe the diffraction/interference pattern. Without the crystal, you get just a small spot on the viewing screen. Over long distances, in principle you'd get effects from diffraction at the aperture of the electron gun, but in practice the electrons repel each other which usually has a larger effect on the spreading of the beam.

 

[DaveC426913]

To make an analogy with light: an unobstructed laser beam follows basically a classical trajectory, but if you put a narrow slit in front of it, you get a diffraction pattern. Looking at the original beam more closely, if you let it propagate a long distance, it spreads because of diffraction at the aperture of the laser.

Similarly, in undergraduate physics labs, a common experiment is to take a narrow beam of electrons (comparable to the ones produced in a CRT), send it through a crystal (lots of narrow "slits") and observe the diffraction/interference pattern. Without the crystal, you get just a small spot on the viewing screen. Over long distances, in principle you'd get effects from diffraction at the aperture of the electron gun, but in practice the electrons repel each other which usually has a larger effect on the spreading of the beam.

Right but let's not mislead the OP into thinking that these beams of light "change" from one form to another. Light, and everything else is both particle and wave simultaneously. It's just a matter of how you look at it.

The question is similar to
At what speed does an accelerating object switch from Newtonian acceleration to relativistic acceleration?

The answer, of course, is: there is no switch. When you are walking down the street, you are obeying relativistic laws it's just vanishingly small.


It might help at this point if someone (who isn't me) explains how macroscopic objects (such as cats and humans) have wave functions and wave-like properties.