Modern physics
 
Category: Modern physics
Diffraction effects are observed when electromagnetic radiation impinges on periodic structures with geometrical variations on the length scale of the wavelength of the radiation. The interatomic distances in crystals and molecules amount to 0.15–0.4 nm which correspond in the electromagnetic spectrum with the wavelength of x-rays having photon energies between 3 and 8 keV. Accordingly, phenomena like constructive and destructive interference should become observable when crystalline and molecular structures are exposed to x-rays.
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Ferrites continue to be a fascinating magnetic material because of their potential applications in high density information, ferro-fluids, magnetic resonance imaging, biomedical diagnostics, drug delivery, high frequency electronic devices, sensors, permanent magnets and magnetic refrigeration system etc [1-5]. Among various ferrites, ZnFe2O4 and CoFe2O4 have been most extensively studied systems, because they exhibit the typically normal and inverse spinel ferrites respectively [6,7]. Zinc ferrite bulk is antiferro magnetic below the Neel temperature (TN = 10K) and turns to ferromagnetic or super paramagnetic when particle size reduces to a nanoscale
1303 days ago
 
crystal lattice was always assumed to be completely rigid, i.e. atomic displacements away from the positions of a perfect lattice were not considered. For this case, we have developed a formalism to compute the electronic ground state for an arbitrary periodic atomic configuration and therewith the total energy of our system. Although it is obvious that the assumption of a completely rigid lattice does not make a lot of sense (it even violates the uncertainty principle),
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In the nearly free electron approximation, interactions between electrons are completely ignored. This model allows use of Bloch's Theorem which states that electrons in a periodic potential have wavefunctions and energies which are periodic in wavevector up to a constant phase shift between neighboring reciprocal lattice vectors.
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Studies on the crystals for solar cells with high conversion efficiency We have fabricated multicrystalline SiGe solar cells with microscopic compositional distribution and proved, for the first time, that SiGe bulk multicrystals with an average Ge composition of 5% gave 1.3 times higher conversion efficiency than Si bulk multicrystals did. We studied the cause of this high efficiency, and concluded that Ge-rich regions in the crystals refracted light and thus elongated effective optical pass increased the absorption coefficient of the cells.
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The experiment on beta spectroscopy introduces the student into the field of special relativity and weak interactions of radioactive decays. With the help of a simple silicon semiconductor spectrometer the continuous spectra of some beta-ray emitters have to be measured and interpreted
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scintillator and photomultiplier tube detector with integrated preamplifier (2), high voltage power supply, Canberra model 2000 power supply, NIM bin, Canberra 2015A amplifier/single channel analyzer module (2), Rutgers P1075 scaler/timer, Canberra model 1446 coincidence module, multichannel analyzer PC board in computer, Maestro Analyzer software, monitor.
1303 days ago
 
The argument for the short range of nuclear forces are 1 Binding energies per nucleon which are roughly constant indicating that nucleons in nuclei interact only with their immediate neighbours. 2 Measurements of distances between nuclei at which nuclear reactions start to occur, these are 1-2 [fm] larger than corresponding nuclear radii.
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Pure gamma emission : The gamma rays emitted by a nucleus in the gamma decay process are monoenergetic for each transition between energy levels. The gamma energies typically range from 2 keV to 7 MeV. Obviously energy must be conserved and momentum must be conserved. Thus, a small recoil energy/momentum is imparted to the daughter nucleus (can generally be ignored). Nevertheless, this energy is small so the energy of the gamma is very close to the energy of the transition.
1303 days ago
 
X-rays are KeV photons. Atomic X-rays are emitted during electronic transitions to the inner shell states in atoms of modest atomic number. These X-rays have characteristic energies related to the atomic number, and each element therefore has a characteristic X-ray spectrum. In this experiment you will use a high resolution solid-state X-ray detector to record the characteristic spectra of several elements, repeat the pioneering work of Moseley relating X-ray energies to atomic number, and also explore the use of X-rays as a diagnostic tool for sample identification
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The essential idea of Rutherford’s theory is to consider the -particle as a charged mass traveling according to the classical equations of motion in the Coulomb field of a nucleus. The dimensions of both the -particle and nucleus are assumed to be small compared to atomic dimensions (10
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Particle astrophysicists have made progress on all of these questions but much work remains I Galactic and extragalactic cosmic rays are not the only energetic particles that we care about: there are also solar energetic particles
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Normal Zeeman effect agrees with the classical theory of Lorentz. Anomalous effect depends on electron spin, and is purely quantum mechanical.
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Electromagnetism is a glorious subject. In its quantum form, it provides the rm foundation of atomic physics, chemistry, materials science, large parts of astrophysics and, of course, electronics and electrical engineering. Having said that, I will not give a self-contained survey of electromagnetism here, since it is covered in other courses. I'll only very brie y survey (or just mention)
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This aspect of the standard emphasizes the critical abilities of analyzing an argument by reviewing current scientific understanding, weighing the evidence, and examining the logic so as to decide which explanations and models are best. In other words, although there may be several plausible explanations, they do not all have equal weight. Students should be able to use scientific criteria to find the preferred explanations.
1303 days ago
 
gravitational “force” varies from point to point and so the acceleration due to this force is not uniform. First consider two particles “side by side” in a gravitational field (see Figure III-1, page 172) directed towards a point (or the center of a sphere). As the particles fall, they will be drawn closer together. Second, consider two particles in a gravitational field which are separated vertically.
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Material objects: objects with inertial mass (i.e., with resistance to acceleration) mass point ⇔ pointlike particle with mass as its only property (ii) Motion through space and time: a few things to know about space and time (in the framework of this course) space: three-dimensional Euclidian space → one can define Cartesian coordinate systems
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According to classical physics, “reality” takes place in a product space R3 × R, where R3 represents space and R represents time. The notions of space and time are axiomatic in classical physics, meaning that they do not deserve a definition. (In relativistic physics, the notions of space and time are intermingled, and one rather speaks about a four dimensional space-time.)
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Astronomy is with mathematics one of the oldest branches of science. It has served as basis for calendars, navigation, has been an important input for religions and was for a long time intertwined with astrology.
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Based on the principles discussed during the last lecture and above, we now know that minerals are composed of atoms, arranged in a specific order, with a well defined chemical composition. We might expect then that the microscopic variations in bond environment discussed above, will also be manifested in macroscopic physical and chemical properties. This is indeed the case
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This kind of backward idea is very harmful to youngsters from developing countries. Partly because of this type of concept, many students from these countries are inclined towards theoretical studies and avoid experimental work. In reality, a theory in natural science can not be without experimental foundations; physics, in particular
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A basic quantity which can be measured for the ground states of nuclei is the atomic mass M(N, Z) of the neutral atom with atomic mass number A and charge Z. Atomic masses are usually tabulated in terms of the mass excess defined by
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Atomic Number or Nuclear Charge: The number of protons in the nucleus. This determines which element is present. It’s the whole number of the element on the periodic chart.
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extending the free electron model to take into account the interaction ofthe electrons witJl the positive ion lattice. In the quantum mechanical free electron (QMFE) model, we assumed that the potential energy inside tJle solid was uniform. It would be more realistic to assume that it is a periodic (alternating W1iformly) function ofx,y,z. This is reasonable because ofthe periodic distribution ofthe lattice ions in a crystalline solid. When the interaction bet\Veen the electrons and tJle lattice ions is considered, we will find some unusual properties possessed by the electrons in the crystal.
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Amplifier requirements are often demanding: • must adapt to specific kinds of signal source and load, • must deliver sufficient gain Single-transistor amplifier stages are very limited in what they can accomplish ⇒ multistage amplifier
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