Fotolistrik

Fotolistrik merupakan peristiwa dipancarkannya elektron ketika permukaan suatu logam disinari cahaya. Elektron yang terlepas dinamakan foto elektron.

Prinsip pengukuran efek fotolistrik.

   

Ada beberapa hal menarik dari percobaan fotolistrik yang tidak dapat diterangkan jika kita menganggap cahaya sebagai gelombang. Hal-hal ini pula yang menyebabkan Einstein mengemukakan teorinya.

1. Hasil percobaan tidak semua frekuensi gelombang cahaya dapat menyebabkan efek fotolistrik. Misal pada logam natrium, jika frekuensi penyinaran <>14 Hz maka tidak akan ada arus walaupun intensitas cahaya diperbesar, padahal menurut teori gelombang, apabila cahaya diperbesar intensitasnya, maka energi gelombang akan bertambah besar yang berakibat energi yang diserap elektron juga bertambah dan arus semakin besar tetapi kenyataannya tidak demikian. Menurut Einstein energi cahaya adalah berupa kuanta yang berarti energinya tidak kontinyu dimana energinya ( E ) diserap oleh tiap partikel elektron sebesar satu energi ( foton ) per elektron sehingga energi elektron akan naik sebesar E = hf , ketika kenaikan energi ini lebih besar daripada energi ikat atom logam, maka elektron akan terlepas begitu pula sebaliknya, apabila E lebih kecil daripada energi ikat atom, maka tidak akan ada arus mengalir. Frekuensi terkecil cahya yang dapat melepaskan elektron disebut f₀ . Sedangkan energinya disebut energi ambang E₀ = hf₀ . Besar energi ambang ini harus sama dengan energi ikat atom Ф = hf₀ yang dinamakan fungsi kerja. Apabila elektron mendapatkan kelebihan energi, maka kelebihan energi ini ,menjadi energi elektron  untuk bergerak yaitu yang menjadi energi kinetik maksimum.

  hf = Ф + (E_k)_max  

2. Ketika frekuensi cahaya lebih besar daripada frekuensi ambang, maka akan dideteksi arus. Tetapi energi kinetik maksimum elektron ini tidak dipengaruhi intensitas, melainkan hanya tergantung pada frekuensi sinar yang datang. Menurut einstein, intensitas yang besar berarti foton yang diserap elektron jumlahnya akan menjadi semakin besar, akibatnya akan makin banyak elektron yang terpental ( jika f > f₀ ). Namun tiap elekteon hanya mendapat "jatah" satu foton saja sehingga energi kinetik dari elektron todak dipengaruhi oleh banyaknya foton yang artinya tidak bergantung dengan intensitas cahaya yang datang. Elektron yang mendapat energi dari cahaya, tidak butuh waktu lama untuk terpental sekitar 10^-9 s bahkan untuk intensitas yang rendah. Menurut Einstein, jika kita mengacu pada teori cahaya sebagai gelombang, akan sulit untuk diterangkan.

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Einstein's relativity theory

General Relativity

    The development of general relativity began with the equivalence principle, under which the states of accelerated motion and being at rest in a gravitational field (for example when standing on the surface of the Earth) are physically identical. The upshot of this is that free fall is inertial motion; an object in free fall is falling because that is how objects move when there is no force being exerted on them, instead of this being due to the force of gravity as is the case in classical mechanics. This is incompatible with classical mechanics and special relativity because in those theories inertially moving objects cannot accelerate with respect to each other, but objects in free fall do so. To resolve this difficulty Einstein first proposed that spacetime is curved. In 1915, he devised the Einstein field equations which relate the curvature of spacetime with the mass, energy, and momentum within it.

    Some of the consequences of general relativity are:
- Clocks run more slowly in regions of lower gravitational potential. This is called gravitational time dilation.
- Orbits precess in a way unexpected in Newton's theory of gravity. (This has been observed in the orbit of              Mercury and in binary pulsars).
- Rays of light bend in the presence of a gravitational field.
- Rotating masses "drag along" the spacetime around them; a phenomenon termed "frame-dragging".
- The Universe is expanding, and the far parts of it are moving away from us faster than the speed of light.

    Technically, general relativity is a metric theory of gravitation whose defining feature is its use of the Einstein field equations. The solutions of the field equations are metric tensors which define the topology of the spacetime and how objects move inertially.

Special Relativity

    Special relativity is a theory of the structure of spacetime. It was introduced in Albert Einstein's 1905 paper "On the Electrodynamics of Moving Bodies" (for the contributions of many other physicists see History of special relativity). Special relativity is based on two postulates which are contradictory in classical mechanics:
    1.The laws of physics are the same for all observers in uniform motion relative to one another (principle of             relativity),
    2.The speed of light in a vacuum is the same for all observers, regardless of their relative motion or of the               motion of the source of the light.

    The resultant theory agrees with experiment better than classical mechanics, e.g. in the Michelson-Morley experiment that supports postulate 2, but also has many surprising consequences. Some of these are:
- Relativity of simultaneity: Two events, simultaneous for one observer, may not be simultaneous for another      observer if the observers are in relative motion.
- Time dilation: Moving clocks are measured to tick more slowly than an observer's "stationary" clock.
   Length contraction: Objects are measured to be shortened in the direction that they are moving with respect    to the observer.
- Mass–energy equivalence: E = mc2, energy and mass are equivalent and transmutable.
- Maximum speed is finite: No physical object or message or field line can travel faster than light.

    The defining feature of special relativity is the replacement of the Galilean transformations of classical mechanics by the Lorentz transformations

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The Theory of Relativity

Two-dimensional projection of a three-dimensional analogy of spacetime curvature described in General Relativity

   The theory of relativity, or simply relativity, encompasses two theories of Albert Einstein: special relativity and general relativity. However, the word relativity is sometimes used in reference to Galilean invariance.

    The term "theory of relativity" was based on the expression "relative theory" used by Max Planck in 1906, who emphasized how the theory uses the principle of relativity. In the discussion section of the same paper Alfred Bucherer used for the first time the expression "theory of relativity".

    The theory of relativity enriched physics and astronomy during the 20th century. When first published, relativity superseded a 200-year-old theory of mechanics elucidated by Isaac Newton. It changed perceptions.

    For example, it overturned the concept of motion from Newton's day, into all motion is relative. Time was no longer uniform and absolute, as related to everyday experience. Furthermore, no longer could physics be understood as space by itself, and time by itself. Instead, an added dimension had to be taken into account with curved spacetime. Time now depended on velocity, and contraction became a fundamental consequence at appropriate speeds.

    In the field of microscopic physics, relativity catalyzed and added an essential depth of knowledge to the science of elementary particles and their fundamental interactions, along with introducing the nuclear age. With relativity, cosmology and astrophysics predicted extraordinary astronomical phenomena such as neutron stars, black holes, and gravitational waves.

    The theory of relativity was representative of more than a single new physical theory. It affected the theories and methodologies across all the physical sciences. However, as stated above, this is more likely perceived as two separate theories. There are some related explanations for this. First, special relativity was published in 1905, and the final form of general relativity was published in 1916.

   Second, special relativity fits with and solves for elementary particles and their interactions, whereas general relativity solves for the cosmological and astrophysical realm (including astronomy).

    Third, special relativity was widely accepted in the physics community by 1920. This theory rapidly became a notable and necessary tool for theorists and experimentalists in the new fields of atomic physics, nuclear physics, and quantum mechanics. Conversely, general relativity did not appear to be as useful. There had appeared to be little applicability for experimentalists as most applications were for astronomical scales. It seemed limited to only making minor corrections to predictions of Newtonian gravitation theory. Its impact was not apparent until the 1930s.

    Finally, the mathematics of general relativity appeared to be incomprehensibly dense. Consequently, only a small number of people in the world, at that time, could fully understand the theory in detail. This remained the case for the next 40 years. Then, at around 1960 a critical resurgence in interest occurred which has resulted in making general relativity central to physics and astronomy. New mathematical techniques applicable to the study of general relativity substantially streamlined calculations. From this, physically discernible concepts were isolated from the mathematical complexity. Also, the discovery of exotic astronomical phenomena in which general relativity was crucially relevant, helped to catalyze this resurgence. The astronomical phenomena included quasars (1963), the 3-kelvin microwave background radiation (1965), pulsars (1967), and the discovery of the first black hole candidates (1971).

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HOW TO CHANGE FACEBOOK LAYOUT

Maybe you want to change your facebook layout because boring with your current layout.If want it, this is step to get it.

1. Install plugin-Add on Yontoo Layers at http://www.yontoo.com/install.aspx, then choose firefox.
2. Choose "accept and continue" in terms of service.
3. Install Yontoo Layers for firefox, then click "start install".
4. Click ALLOW at up right corner, if it is there.
5. Click "install now" after you've done "restart firefox".
6. Login to your facebook account.
7. Click http://apps.facebook.com/pagerage/.
8. Click ALLOW.
9. Then you just choose layout that you want, and your new layout have been ready.

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Albert Einstein
"Einstein" redirects here. For other uses, see Einstein (disambiguation).

Albert Einstein (pronounced /ˈælbərt ˈaɪnstaɪn/; German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist. He is best known for his theory of relativity and specifically mass–energy equivalence, expressed by the equation E = mc2. Einstein received the 1921 Nobel Prize in Physics "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect."[1]
Einstein's many contributions to physics include:

• The special theory of relativity, which reconciled mechanics with electromagnetism
  
• The general theory of relativity, a new theory of gravitation obeying the equivalence principle.
  
• Founding of relativistic cosmology with a cosmological constant
  
• The first post-Newtonian expansion, explaining the perihelion advance of planet Mercury
  
• Prediction of the deflection of light by gravity and gravitational lensing
  
• An explanation for capillary action
  
• The first fluctuation dissipation theorem which explained the Brownian movement of molecules
  
• The photon theory and wave-particle duality derived from the thermodynamic properties of light
  
• The quantum theory of atomic motion in solids
  
• Zero-point energy
  
• The semiclassical version of the Schrodinger equation
  
• Relations for atomic transition probabilities which predicted stimulated emission
  
• The quantum theory of a monatomic gas which predicted Bose-Einstein condensation
  
• The EPR paradox
  
• A program for a unified field theory
  
• The geometrization of fundamental physics.
  

Einstein published more than 300 scientific works and more than 150 non-scientific works.[2][3] In 1999 Time magazine named him the Person of the Century, and in the words of a biographer, "to the scientifically literate and the public at large, Einstein is synonymous with genius."[4]:159

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