Why does the glow disappear at 0.01mm of Hg inside the tube which results into darkness??

Discharge Tube Experiment

 

Why does the glow disappear at 0.01mm of Hg inside the tube which results into darkness??

 

 

Presumably your experiment studied the effect of steadily evacuating the tube?

 

More detail would have been helpful.

 

Then you would have seen at higher pressures a continuous glow between the electrodes.

 

As you reduce pressure to about 0.1mm of mercury the glow becomes striated (breaks up to glowing and dark bands).

 

These bands are not all of the same size.

There is one quite large one near the cathode called the Faraday dark space, shown in the picture.

Another large one is the Crookes dark space.

 

 

As you reduce the pressure further the gaps become larger and the glow zones smaller.

 

until, in your case your reach a point where the pressure is so low that the gaps overtake the glow zones.

 

 

Now since this presumably coursework you want to know why.

 

So think about the question

 

What glows?

 

And what are you removing when you reduce the pressure?

 

Test your answer here before reporting the experiment.

 

The original experiment was carried out by

 

De La Rue and Muller in 1878

 

Later work in the spectroscopic aspect was due to Paschen.

 

You might like to look these up, especially the latter as you have posted in Chemistry, not Physics?

Edited June 3, 20178 yr by studiot