How Does Changing Plate Distance Affect Interference Patterns in Interferometry?

[binbagsss]

- why is it that fewer rings are observed when the plates are moved closer together (given wavelength , monochromatic source). What equation shows this relation?

- Consider a non-monochromatic source, such as a Sodium Lamp, as the distance varies, both patterns change but at different rates - one will change at a faster rate than the other - which one changes quicker - the D line with the greater or smaller wavelength? And why is this, again is there an equation to show this relation?

- As the distance between the plates is changed, the number of rings observed changes also - are there any other observable affects varying with this distance?

Thanks a lot anyone for any assistance !

 

[Simon Bridge]

also see: your other thread about this interferometer for the context.

- why is it that fewer rings are observed when the plates are moved closer together (given wavelength , monochromatic source). What equation shows this relation?

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/fabry.html
Take a look at the geometry panel - when the path difference (length CD) is an integer number of wavelengths you get constructive interference and thus a maxima. CD depends on the angle and how far apart the plates are by simple geometry.

To understand this - sketch the diagram with different plate separations.

- Consider a non-monochromatic source, such as a Sodium Lamp, as the distance varies, both patterns change but at different rates - one will change at a faster rate than the other - which one changes quicker - the D line with the greater or smaller wavelength? And why is this, again is there an equation to show this relation?

Again, it is the path difference equation ... the path difference needs to be a whole number of wavelengths.
Work it out.

- As the distance between the plates is changed, the number of rings observed changes also - are there any other observable affects varying with this distance?

What sort of effect did you have in mind?