VCE 07

[jules]

Just a couple of questions in VCE 07

In the light and matter section,

The neutron beam is projected onto a metal crystal with interatomic spacing of 3* 10^-10
Would you expect to observe a diffraction pattern?  Explain.
(the de Broglie pattern is 2* 10^-10

When using wavelength over width formula, the ratio is 2/3, yet in the answers it says there will be a diffraction pattern?
Could some please explain?

Also the last question:

State the electron mechanism in each of the sources below that produces each spectrum:

Incandescent Light Globe

Mercury Vapour Lamp

Could someone please explain that as well?
Cheers.

[Fireworks]

When using wavelength over width formula, the ratio is 2/3, yet in the answers it says there will be a diffraction pattern?
Could some please explain?

Was it of the same order? I think if the
ratio is of the same order, you are expected to state that diffraction will
be observable. By the same order, I mean like if one wavelength was 2*10-21/3*10-21;
Diffraction would be observable.

[wilfred]

The wavelength over width formula just has to be close to one for diffraction to be observed, but it is more prominent when the ratio is grater than one though.
Incandescent Light Globe: Atoms in the filament are excited by heating, the electrons are accelerated and they collide, when an electron is accelerated it releases energy as a wave, due to the random nature of this it produces a broad spectrum.\
Mercury Vapour Lamp: Produces light through quantized energy levels, therefore there are a set energy levels and only certain photons can be emitted. That means only discrete wavelengths are emitted