LASER
>> Sunday, November 14, 2010
Today, lasers can be found almost everywhere, from telephone lines to cutting edge scientific research, supermarket scanners, and even cat toys.The first laser light was produced on May 16, 1960 at the Hughes Research Lab in Malibu, California when Theodore Maiman switched on his fist-sized device that flashed a bright red spot onto a photo-detector. Since then, lasers have become smaller, more powerful, and ubiquitous in modern technology.
Lasers have had an especially big impact on information technology. Sending data using digitized laser light signals over fiber optics has revolutionized the transfer of data. The IBM Roadrunner, the world's second fastest supercomputer, has over 45,000 lasers used for sending data across its 133,000 processing cores. Likewise, fiber optics make up the backbone of the Internet as nearly all data runs on fiber optic lines.
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The Sun
>> Friday, September 3, 2010
Fact about The sun
1. The age of the Sun is about 4.5 billion years. The location of Sun in Our solar system is on the edge of a spiral arm called Orion's Arm, and is one-half to two-thirds of the way (28,000 light-years) from the center of our Milky Way galaxy. The Sun, an ordinary star, contains more than 99.8% of the total mass of our solar system. The amount of the Sun's energy reaching the Earth's atmosphere (known as the Solar constant) is equivalent to 1.37 kw of electricity per square metre
The energy in the sunlight we see today started out in the core of the Sun 30,000 years ago - it spent most of this time passing through the dense atoms that make the sun and just 8 minutes to reach us once it had left the Sun
The Sun is our closest star and the centre of the Solar System. It is around four and a half thousand million years old and in 6 thousand million years or so, it is predicted that it will reach the end of its life (more on that further down). Currently however, it is an 'average' sized star, classified as a G2 type main sequence star. These can be found quite abundantly throughout the visible universe.
However, don't let this apparent 'normalness' of the Sun's size in comparison with other stars fool you - compared with anything else in our solar system, it is absolutely superlative. To give you an idea of its size, it has 333,400 times more mass than the Earth and contains 99.86% of the mass of the entire Solar System - this means Jupiter and all the other planets and asteroids put together only account for 0.14% of the mass of the Solar System. The Sun's core is so hot and dense that just a pinhead of its material could kill a person 160 kilometres away.
Every second the Sun loses 4.5 million tonnes of material, blown off to space - this means that in 42 million years it would lose enough material to make the Earth. However this high loss rate of mass is really rather insignificant when compared to the total mass of the Sun - over the past 4,500 million years it has barely lost a few hundredths of a percent of its total mass. Interestingly, all the light we see from the Sun comes from a layer 500km deep (the top 0.1%) and takes about 8.3 minutes to reach us down here on Earth. By contrast, radiation from its core takes about 170,000 years to make its way out to the surface, due to the high density of the mass it must travel through.
Viewed from the surface of the Earth, to normal human beings the Sun appears to be a simple, round uniform yellow ball. When observed in detail however, as the pictures show, this is far from being the case. In reality it has several well-defined layers leading up its surface, and above its surface it even has what could be termed it's atmosphere - the mystifyingly scorching hot solar corona.
An imaginary solar 'tourist', travelling out from the centre of the Sun, would begin his journey at a sweltering 15.6million°K in the core, gradually decreasing as he got further from the centre, eventually reaching just 5780 or so Kelvins in the photosphere - the Sun's 'surface'. However, the temperature would then begin to increase as he progresses through the Chromosphere, up to 10,000K, culminating in an a massive 1 million K (or higher) in the corona! The exact reason for this unexpectedly high temperature in the corona is still unknown, though recent research has ascertained that the energy needed to heat the corona to such high temperatures is somehow provided by the Sun's vast magnetic field.
The Sun was born, as mentioned earlier, about 4.5 thousand million years ago. Like all stars, it was formed when a cloud of gas of at least 100 Solar Masses, floating around the galaxy, got squeezed by an outside influence (e.g. a nearby supernova explosion or the pressure of a passing spiral arm of the galaxy) and started to collapse. After a while, the cloud (or 'nebula') would have reached a point at which it continued collapsing under its own weight, breaking up in the process to form many different stars. As the part that was to be the Sun collapsed further, it became more and more dense and increased in temperature. Under the increasingly strong influence of a central gravitational force, the mass would soon have formed a spherical shape, and when the temperature in the centre reached about 15 million°C, it got hot enough for nuclear reactions to start. The outward force created by these reactions acted as a stabilizing influence on the star, preventing further collapse, so the star eventually reached an equilibrium.
Nuclear Fusion
The Sun is now a stable star, though gradually increasing in luminosity. It is presently 'burning' hydrogen in its core, converting it into Helium by a nuclear fusion process. And here's where the extremely high temperature and pressure present in the core of the Sun comes in, for these conditions make it impossible for whole atoms to exist - instead the protons and electrons forming atoms are free to move sperately, thereby forming a plasma in the Solar core. The immense pressure of the Sun's weight then acts to push the protons and electrons closer together than they would be normally, and eventually to fuse together 4 Hydrogen nuclei (ie 4 protons), in a number of stages,
to end up with 1 helium nucleus (ie 2 protons and 2 neutrons).
However, the Helium nucleus formed actually contains very slightly less mass than
the 4 protons which formed it. This is because the rest of the mass is converted into pure energy in the ratio E=mc². This simple reaction, occurring on a vast scale inside the Sun's core, produces absolutely vast amounts of energy, and is the source of all electromagnetic radiation (and heat) coming from the Sun.
In fact about 700 million tons of Hydrogen are converted to Helium every second, releasing 5 million tons of pure energy.
The Sun's Future
However nuclear fusion can only keep happening for another four thousand million years or so, when Hydrogen will then run out in the core. When this happens the inner core will shrink and the Sun will expand and get hotter, due to Hydrogen being 'burned' in the outer core, engulfing Mercury and nearly reaching Venus. As it does so, the core will reach a blistering 100 million°C and will begin to burn the Helium there. This will keep the star stable as a 'Red Giant' for a thousand million years or so until the Helium runs out. When this happens, the core will begin collapsing again and it'll get hotter and the star will get bigger once more, expanding to the present orbit of Earth.
At this point, the Sun will be very unstable, expanding and shrinking often and losing a lot of material into space. Soon afterwards, all that will be left will be its inner Carbon core, which, although it will still contain about 2 thirds of the Sun's mass, will be collapsed so much that it will have reached the ultimate density, quantum forces will stop it collapsing further and it'll become a 'White Dwarf' - a small star about the size of the Earth but much denser (about 1cm3 of this stuff would have the mass of a tonne - that's a million times the density of water!)
Majlis Anugerah Cemerlang
>> Sunday, April 25, 2010
Tahniah kepada semua pelajar yang mendapat pelbagai anugerah MAC 2010 terutama kepada 12 orang pelajar yang mendapat fizik A-, A dan A+
Refraction, sunrise, sunset
>> Monday, February 22, 2010
Due to refraction :
- The sun will appear to rise sooner (by approximately two minutes) than it actually does
- The sun will appear to set a bit later (by about two minutes) than it actually does
>> Thursday, February 4, 2010
Lightning may not seem much like static electricity, but it's actually very similar. Both are sparks of electricity created through the attraction of unlike charges. The difference is that static electricity
creates a small spark, while lightning is a huge spark of electricity.In storm clouds, tiny particles in the cloud move around picking up positive or negative energy charges, like when shoes scuff a rug. The positive charged particles stay light, and rise to the top of the cloud. The negative charged particles get heavier, and collect at the bottom of the cloud.
As more particles become charged, they divide into opposing groups in the cloud. When the power of attraction between them gets too great, the particles discharge their energy at each other, completing a path for electricity to travel through the air. We call this flow of electricity lightning.
It's the negative charges in the bottom of the cloud that cause lightning to strike the ground. When the negatively charged particles group together, they begin to seek out positive charges from the ground below. The excess electrons create a channel of charged air called a leader that reaches down to the ground below. The leaders attract other charged ground-based channels called streamers.
When the stepped leader from the cloud meets a returning streamer from the ground, the path is ready. An electrical current called the return stroke, travels back up the path. This return stroke releases tremendous energy, bright light and thunder.
The typical stroke can last only 30 milliseconds, so four to five strokes may happen in the blink of an eye. Despite the old saying, lightning does strike the same place twice.
To review, lightning is created by the attraction between opposite charges, the same force that creates static electricity. But lightning uses huge opposite charges to produce an electrical current that's nothing like what you'd get from static electricity.
>> Friday, January 29, 2010
Stars
On a clear dark night, a few thousand stars are visible to the naked eye. With
binoculars and powerful telescopes, we can see so many stars that we could never hope to count them. Even though each individual star is unique, all stars share much in common. The Sun, which is the source of virtually all light, heat and energy reaching the Earth, is the nearest star. Today, we know that stars are born from interstellar gas clouds, shine by nuclear fusion and then die, sometimes in dramatic ways.
Globular Cluster M3.
Some 500,000 stars are
crammed into an region about
100 light years across in
this globular cluster
Why do stars twinkle?
The songline goes "Twinkle twinkle little star". What is the cause of the "twinkling" of stars? Does light from planets "twinkle" as does light from stars?
Stars twinkle because of turbulence in the atmosphere of the Earth. As the atmosphere churns, the light from the star is refracted in different directions. This causes the star's image to change slightly in brightness and position, hence "twinkle." This is one of the reasons the Hubble telescope is so successful: in space, there is no atmosphere to make the stars twinkle, allowing a much better image to be obtained.
Planets do not twinkle the way stars do. In fact, this is a good way of figuring out if a particular object you see in the sky is a planet or a star. The reason is that stars are so far away that they are essentially points of light on the sky, while planets actually have finite size. The size of a planet on the sky in a sense "averages out" the turbulent effects of the atmosphere, presenting a relatively stable image to the eye.
Read more...
The songline goes "Twinkle twinkle little star". What is the cause of the "twinkling" of stars? Does light from planets "twinkle" as does light from stars?
Stars twinkle because of turbulence in the atmosphere of the Earth. As the atmosphere churns, the light from the star is refracted in different directions. This causes the star's image to change slightly in brightness and position, hence "twinkle." This is one of the reasons the Hubble telescope is so successful: in space, there is no atmosphere to make the stars twinkle, allowing a much better image to be obtained.
Planets do not twinkle the way stars do. In fact, this is a good way of figuring out if a particular object you see in the sky is a planet or a star. The reason is that stars are so far away that they are essentially points of light on the sky, while planets actually have finite size. The size of a planet on the sky in a sense "averages out" the turbulent effects of the atmosphere, presenting a relatively stable image to the eye.
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