ZaKi AbaaS
مؤسس المنتدى
عدد الرسائل : 91
العمر : 53
البلد : ismailia
العمل/الترفيه : التربية والتعليم
المزاج : رايق
تاريخ التسجيل : 18/11/2007
 |  موضوع: Chapter 12 : Wave paticle Duality  السبت يناير 12, 2008 2:31 am | |
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1) Classical physics connot explain many phenomena particularly those in which light (or em radiation) interacts with electrons or atoms.
2) Light or any em radiation consists of a huge collection of photons, each photon having energy hn, where h is Planck's constant and n is the frequency.
3) An evidence for photons is the photoelectric effect) where photocurrent depends on the inensity of incident light as long as the frequency is greater than a critical value nc. But if the frequency is less than nc , no photo current flows. The kinetic energy of the electron freed by the photoelectric effect depends on the frequency not on the light intensity.
4) Photon has a mass, a linear momentum and a constant speed which is the speed of light. It has a size denoted by the wavelength. If a photon falls on a wall, it applies a small force on it, but if it falls on an electron, the electron will be thrown off due to its small mass and size.
5) Compton effect proves the particle nature of photons, where a photon has mass, speed and linear momentum.
6) A wave describes the collective behavior of photons.
7) The wave length of a photon is Planck's constant divided by the linear momentum. The same relation applies to a free particle, where the wavelength describes the wave nature of the particle, i.e., the wave accompanying the particle.
 The electron microsocpe proves de Broglie's relation for particles. It is used to detect diminutive particles.
9) Quantum mechanics is based on assumptions which agree with experimental observations, for the cases when an electron is trapped within limited confienmet. While classical physics applies when the electron is free to move or when the contining size is extensive.
Basic Laws::
1- E= hn
E: energy of photon, h planck's constant.
h = 6.626 x 10-34 Js, n frequency Hz
Photoelectric Effect: Einstein proposed the following:
The energy needed to free an electron from a metal surface (called the work fucntion) is Ew = E= hnc
nc is the threshold (critical value) of the frequency, of the incident photon.
b- If the photon energy exceeds this limit, the electron is freed and the energy difference (hn - Ew) is carried by the electron as KE.
c- If hn < Ew, the electron would not be emitted at all, no matter how intense the light might be.
d- nc and Ew vary for different materials and do not depend on the light intensity, the exposure time, or the voltage difference between the anode and the cathode.
3- Photon properties:
a- Photon is a concnetrated packet of energy which has mass, velocity and linear momentum.
b- Its enegry E = hn
c- It always moves at the speed of light C = 3 x108 m/s, regardless of its frequency.
d- The photon has a mass of hn / C2, while in motion.
e- The photon linear momentus is hn / C = PL
4- Einstein showed that mass and energy are equivalent E = mC2.
5-The force which a beam of photns applies to the surface is the change in linear momentum per second:
6- 
Where Pw in the power is watt of the light incident on the surface. This force is appreciable if it affect a free electron, so it throws it off. This is the explanation of compton effect.
10- Wave properties of matter:
De Broglie put a hypothesis of wave particle duality to particles, the wave length of a prticle must be in analogy with a photon
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