Observations in the cathode ray tube experiement 
1.One of the observations I learned was that the glass tube begins to glow with a brilliant green light. Many websites I read through refer to a fluorescent material. However, as shown in the above diagram there was no fluorescent material in the experiment carried out first on the cathode ray tube. So where does the green glow come from. Is this the color of the radiation itself?
2."Cathode rays travel in straight lines. That is why, cathode rays cast shadow of any solid object placed in their path. The path cathode rays travel is not affected by the position of the anode." I just can't seem to understand this explanation of the one of the observations.Also, different websites analyses this observation differently. For example, " The cathode rays consist of material particles because they produced shadow of objects placed in the way"
3.Two of the conditions of the experiment were air at very low pressure and secondly a very high potential difference. Could someone please tell me why these conditions were necessary?
I know the questions are very silly but because different websites refer to different things, I am becoming confused with something that should be simple to understand.
 A: The light emitted from the electron stream comes from nitrogen and oxygen molecules.  Green is mostly from oxygen.  The negative electrons are pulled strongly enough by the positively charged anode that they whack the electrons in the O2 and N2 molecules, putting them into higher energy states or knocking them free of the molecule.  In a short time, seconds or a fraction of a second, these electrons rejoin the ionized molecules, fall back into the ground states through one or more quantum decays emitting photons.  
Note that the concept of flourescence isn't relevent.
For the electrons emitted by the cathode to do this, they need enough oomph.  How fast they move is determined by the strength of the electric field.  A stronger field is made by a higher voltage difference applied to the anode and cathode.  This is usually much stronger than needed to merely ionize air molecules - we want to those electrons to fly to the anode rather than be scattered by their interactions with the molecules.
To have the electron-molecule interactions, of course we need molecules. That's why the glass tube isn't just a plain vacuum.  It can't be air at normal pressure, because that would be too many molecules in the paths of the electrons.  The electrons would be deflected and lose a small part of their kinetic energy with each interaction.  Normal air suitable for everyday human use would involve so many interactions in a short distance, the electrons be scrambled into a fuzzy cloud of plasma, and not make it to the anode but by an uninteresting, undramatic process of diffusion through the air.  You'd see a small area of glow right around the cathode, perhaps, depending on conditions.   So, we need a bit of air so something interesting happens, but not enough that it gets in the way.
The electrons travel in straight lines (or nearly straight curves) because the electric field between the anode and cathode is approximately uniform, that is, straight lines.  Like a ball falling in gravity, the electrons are on parabolas, but there isn't much transverse velocity, so like a ball falling straight down, the parabolas are just lines.  Also, the low-pressure air tends to put a limit on the electrons' speeds, affecting the electrons' motions to more closely follow the electric field.
Nice explanation of molecular excitations at http://www.atoptics.co.uk/highsky/auror3.htm 
A: Notice the "Air at very low pressure"? That thin air is what glows. And it has to be very thin or it disrupts the "ray" nature of the phenomena. I'm not sure what exactly was glowing in the earliest experiments, but it might well be the $\mathrm{N}_2$. 
Later it was normal to put some mercury in the tubes because it works really well. In fact, that is what a florescent light is: a mercury vapor lamp (generally with some phosphors on the glass to get a nicer spectrum).
A: In this experiment  discharge glass tube was taken and at both end of glass two metal plate were placed. they were connected with high voltage battery(10000 volt.) the H2 WAS filled at high pressure and  at anode end a layer of ZnS WAS placed.
1) At high pressure i.e. 1atm when high voltage current passed then no change seen in the tube. it is because gas is poor conductor of electricity
2) At low pressure i.e. 1torr when high voltage current passed through tube then a greenish glow is seed on ZnS screen. it is because the molecules get ionized and some negatively charge particle travels from cathode plate to anode plate in form of invisible ray called cathode rays>
3) At very low pressure when high voltage current passed thorgh tube then tube became dark. it is because at very low pressure the scattering of light does not take places.
charge/mass ratio of cathode ray is 1.74*10 power 8 c/gram
