October 31, 2016 Monday
Bedtime Story
The Physics of CRT RAM
The Physics of CRT RAM
By the end of the war, the idea of an electronic computing machine
had been firmly established due to the likes of Alan Turing, Alonzo Church,
Tommy Flowers (designer of the Collosus series at the Bletchley Park), John von
Neumann among others.
One among many hindrances in the development of a computing
machine was the absence of means of storing instructions or data.
It was in the immediate post-war years of 1946-47 that these 2 men
came up with the invention that carries their name and is called the
Williams-Kilburn tube.
Ask yourself how a scintillating screen that is coated with
phosphor can store information.
Just thinking about a problem without coming to an answer is a
reward in itself as it can make life very exhilarating and meaningful.
Let us consider what happens when a beam of electron or rather a
single electron hits the phosphor coated screen on the cathode ray tube.
When an electron hits the phosphor atom (with added impurities),
it exhibits the phenomenon of fluorescence.
Fluorescence is essentially absorption of electromagnetic energy
of high energy and release of energy of low energy that is explained by the
quantum nature of arrangement of electrons in an atom.
So we see a glow in the cathode ray tube.
That is a well understood by anybody who has attended his physics
laboratory during his high school science courses.
When the beam of electrons having energy beyond certain threshold
and hits a phosphor atom, then the phosphor atom besides releasing
electromagnetic energy of lower frequency may end up releasing or losing an
electron.
This in physics is known as secondary emission and the electrons
released are known as secondary electrons.
These released electrons do not possess sufficient energy or
momentum to fly away too far and hence fall back after travelling a short
distance.
During that short duration of time before their emission and
recapture back by the coated surface, in that spot for a very brief period a
relative positive charge is created.
Technically it is known as a charge well or the potential well.
We are talking of extremely small dimensions where quantum
mechanical behavior takes over.
These 2 bright men Kilburn and Williams realized that this charge
well so created can be used to represent a single binary digit.
Stay tuned to the voice of
an average story storytelling chimpanzee or login at http://panarrans.blogspot.in/
Good night and my fellow cousin ape.
Another great educator and a teacher that I am aware of is
Professor Subhashish Chattopadhyay in Bangalore, India.
While I narrate stories, Professor Subhashish an IIT graduate and
a former professor at BARC, does and teaches real mathematics and physics.
He started the participation of Indian students at the
International Physics Olympiad.
Do visit him here:
All his books can be downloaded for free through this link:
For edutainment and English education of your children, may I
suggest this large collection of Kids Songs:
Basic circuit of a CRT RAM
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