polarised electron beam

Q: what is a polarised electron beam?

A: A polarized electron beam means that the spins (the spin represents the angular momentum of an electron) of all electrons are in the same direction.

Q: what is monoenergetic?

A: As the name implies, "mono-energetic" means single energy. It means that all electrons possess the same energy.

Q: why must the electron beam be approximately monoenergetic?

A: The "electron diffraction" experiment is an illustration on the "wave nature" of electrons, as diffraction is a wave property.

To obtain a clear diffraction pattern, it is best to have the wave be of a single wavelength. When transpired to electrons, this implies that the electrons should have a single energy.

I don't think this is an AL question.

'Polarized electron beam' means that the electron wave is polarized and 'monoenergetic' means that all the electrons emitted carry the same energy.

2013-04-03 23:37:31 補充：
The electrons need to possess the same amount of energy because they need to have the same wavelength to produce an observable diffraction pattern.

2013-04-04 18:03:51 補充：
Polarization is a feature of transverse wave where the oscillation of particles (or electric field for EM wave) is restricted to a single plane. Please check if this is in your syllabus.
Electrons having different wavelength will suffer different degree of diffraction through the copper coil,

2013-04-04 18:05:57 補充：
and as a result producing an unrecognizable diffraction pattern.
I choose 'opinion function' because I am not good at physics and afraid of providing an incorrect answer.
I just hope to give my opinion.