On Spectrograph from Compact Disc (Part I)

Image (top) shows a sample of vinyl record and image (bottom) shows the groove of the record disc.

Compact Disc (CD-ROM) or its relative cousins like DVD and Blu-Ray discs works on same physical operating principle similar to the earlier vinyl records where information is etched on a trench shaped groove in spirals on the disc. A needle from the reader machine (like a gramophone player) called the stylus is then placed on one of those grooves. As the vinyl disc rotates, the stylus plough through the groove and the analogue information stored as features on the trench is then converted to electrical signals which is then electrically amplified to produce sound at output speakers which we perceive as audio recordings.

Image (top) shows logo and a sample of Compact Disc and image (bottom) shows microscopic image of the "broken groove" which composed of many tiny "pits" among a flat "land".

In essence, Compact Discs shares similar working principle with the vinyl record except that the grooves in CDs are much smaller. The reader of CDs have stylus but instead of materials, it is a beam of bright light, i.e. laser. A layer of reflective surface is applied to the top-most layer of the CD. The information stored is being "burned" into many tiny holes called pits on the flat plastic below the reflective disc surface called "land". These on and off pits formed a spiral of broken trench like the vinyl record. When laser light is shone on the bottom surface (where the pits and land is located), the difference in height between the pits and land will produce a reflection of light in different intensity which is detected by the reader. These changes of light intensity is then converted to digital signals, which then being processed to produce audio or video outputs.

On Lights From Masking Tapes

About a few weeks back while I was in the dark room preparing small square pieces of x-ray films, I discovered something interesting. The x-ray films are used in plasma-focus diagnostics but that's outside of this story.

What happened was, after preparing those light-sensitive x-ray films, I have to keep them in a light tight pocket. Because x-rays can penetrate the pocket material (usually a black pvc or in my case, a home-made black paper envelope) the films contained inside the pocket will register an image depending on the intensity of the x-ray, just like ordinary films.

Now, making the paper envelope requires a type of adhesive, so I used masking tape. Since I did this in a dark environment, it led me to observe something I could not understand at first.

So this is what happened:

The moment force is applied to the peeled tape, a layer of tape is lifted from the roll. What I saw was a momentary emission of bluish-white light coming out from the contact between peeled tape and the roll. This light only emits when the tape is pulled in a sudden. Astounded by this discovery, I kept repeating it to see if there are changes when I applied force of different magnitude (strength). The colour of the light is the same, but the intensity increases with increasing applied force.

So that night I went online to search what was it and I came across this from nature.com. It appears, if I were to perform this in a vacuum condition I would get x-rays! (what's more is that the x-ray intensity would be high enough to take x-ray images of a human thumb!)

Now since I was working in a plasma technology lab, I asked my supervisor if she's able to provide me a chamber for this test (and they have x-ray detecting diodes too) but she said the set-up is too time costly and took this as a novelty phenomenon.

Well, If I have a lab myself.

It appears that visible light I saw was generated from an effect called triboluminescence, which is an effect where light is emitted when solid material is given a mechanical stress such that chemical bonds are broken/altered to produce light.

Detailed information can be obtained from Wiki.

Big Bang: How The Universe Appeared From Nothing

Here's a cool video on explaining a possibility of the creation of our Universe. I got this link from Main Sequence and thought it would be awesome to share it out!

In the beginning, there was nothing and the idea of nothingness is difficult to put into picture because it is after all, well, completely nothing. Talk about space, not just the distance between stars but also the distance right in front of your eyes, the matter, and energy and light, these all don't exist in the pre-Big Bang history. So, the question was (and still is) Where did all these wonders came from?

Quantum mechanics provides an insight, that at the very early universe when all things are crushed into a tiny point (refer to my previous posts on the big bang), quantum mechanics must have played an important role in the formation process of our cosmos.

Fundamentals of X-Ray Generation

This video explains one of the earliest method of X-ray generation from the heating of filaments in a high vacuum and the usage of high voltages.

The act of getting electrons from heating a filament in high/partial vacuum is called "Thermionic Emissions" where the electrons in the filament is being "boiled" off from the filament metal due high temperature.

Image du jour #3: Lunar Eclipse 2011

CLICK IMAGE TO ENLARGE

This is a compilation of photos taken from my digital camera showing in a time lapse of 7 minutes and the phases of the shadowing of moon observed from the living room in my house, convenient much! especially totality (full eclipse of moon) occurred around 3.25am local time. Because the photos are taken without any magnification, the image we see is in fact a small cut-out, enlarged from a relatively high pixel camera. (from my DSLR). This leads to the badly resolved grains seen in the images.

Lunar eclipse occur when the sun, earth and moon are perfectly arranged in a straight line where the earth is in the middle, therefore lunar eclipse can only occur in the night of full moon. The length of lunar eclipse is much longer than solar eclipse is because of the relative size of the moon compared to earth. Think about it it this way:

You're inside your car waiting for the traffic light to turn green. Now you look ahead across the crossroad junction and you saw a an interesting person who catches your eye. (Say, a beautiful lady). Now it is the turn for the east side of the junction to move, and cars are passing in front of you. When a small car passes in front of you, you'll have to wait until the car passes through before you're able to see that lady in front. A car is much smaller than a bus, so, when a bus took its time to cross the road, perhaps that person has already slipped through your eyes, and there's that "oh-well" sigh.

Similarly, lunar eclipse happen because the earth is blocking the sun's light (in the analogy, the beautiful lady being the light source - sun), and solar eclipse is the moon blocking the sun's light. Since the moon is much smaller than the earth, naturally the length of lunar eclipse is much longer compared to solar eclipse.

Another interesting fact explains the mystery why the moon does not completely disappear but instead, appears to be amber or sometimes coppery-red when totality occurs. This is interesting because during solar eclipse, all that we see is a sun being 'eaten' by the moon and nothing in particular happened on the dark shadowed area of the sun.

In a lunar eclipse, the earth blocked the sun's ray. But the earth does not completely block all the light from the sun. A little part of the sunlight passed through the surface of the earth and the light is refracted due to earth's atmosphere which acts like a prism. (refraction of light is the same process that produced the rainbow where the water in the air acts like a prism which split light from sun into the familiar rainbow colours) The refraction of light produced a rainbow likened light which consist of mostly red and blue. This light is then beamed to the moon where during totality (when moon is completely shadowed by earth), the red part of that refracted light hit the surface of the moon, hence the red appearance.

The explanation of the light rays can be better explained graphically HERE.

Cosmic Rays: Concerns on Exposures

#Here's a quick (and also the final segment) continuation from yesterday's post.

Although effects of ground level radiation exposure to cosmic rays are minimal to health, on high altitudes however, the radiation level is becoming a concern. (refer to the first graph on the last post)

Studies in the past have shown that commercial flight crews will receive more than 1 milli-sievert (mSv) which is the general public’s limit of radiation exposure limit. A round trip from Thailand to New York will result 0.28 mSv, which is about 10 times more than an exposure of a lung x-ray machine.Some transatlantic flight crews are even required to wear a radiation dosage badge to indicate the amount of exposures they receive on the trip.

Excessive exposures to radiation will result in the alteration of genetics and hence lead to cancer. This topic will be discussed next time.

Cosmic Rays: Interactions of Particles with Earth's Atmosphere

The count rate of particles vs. the altitude of earth’s atmosphere (hyperphysics.phy-astr.gsu.edu, 2010)

When a primary cosmic ray particle enters earth atmosphere, it will encounter many atoms and collisions will occur. This collisions will send a shower of “secondary” particles which are also subatomic particles such as pions which will quickly decay into relatively stable muons, neutrinos and gamma rays. Muons will soon too decay into electron and positrons which they both will annihilate and the gamma rays will interact with atmospheric atoms.

The numbers of particle that finally reached the earth’s surface depends on the energy content of the "primary" cosmic ray particle. Most secondary cosmic rays that reached the surface of earth are muons with an average intensity of 100 counts per metre square per second.

Although thousands of cosmic ray particles pass through our body every minute, the resulting exposure to that amount of radiation is minimal, safe, and is considered as background. We can say that we are irradiated with fast particles every single moment in our lifetime with negligible health effects.