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Physical Background
Diffraction, which arises in closeness of obstacle when light passes from point source, was investigated by Fresnel. In this phenomenon, which is called Fresnel’s diffraction, we face the problem of interference of spherical waves, based on Huygens principle. If we consider diffraction from distant source (monochromatic coherrent light), wavefront is nearly flat. We approach to phenomenon, which arise by diffraction of parallel beams with planar wavefronts, which are called Fraunhofer’s diffraction.
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Weather data - the temperature, the pressure and the intensity of sunshine - are monitored for demonstration of the remote sensing experiment. The thermometer unit of ISES measures the temperature with the accuracy of about 1 %. The atmospheric pressure is measured by the pressure measuring unit of ISES and recalculated to the sea level (as a correction of our elevation above the sea-level). The light intensity unit from ISES is the simple uncorrected light sensor unit of ISES. It is directed to the free sky in the East direction. Data are collected every 10 s and are stored on hard disc of the server from where you can download it.
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Physical Background
Electromagnetic induction is the phenomenon of the mutual coupling of the magnetic and electric fields, where the electric field is generated whenever a time varying magnetic field is present. For example, in the introductory experiment in the picture above there is a bar magnet moving in the direction of the winding and thus creating the time dependent magnetic field. We can observe the deviation on the connected measuring instrument. This deviation is caused by the time dependent electric field in the coil. This phenomenon is called electromagnetic induction. Electromagnetic induction is used for example in dynamos or alternators, which are the devices for transforming mechanical energy into electrical one. For the quantitative description of the experiment we need to introduce a few physical quantities and symbols.
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Physical Background
A body making an oscillatory harmonic motion is called the harmonic oscillator. At the first approximation it may be e.g. a body suspended on a spring (Fig. 1) or an atom or a molecule of a solid. If the damping resistance of the environment may be neglected, we speak about the undamped harmonic oscillator. We can demonstrate that the oscillation is harmonic, if the acting force is proportional to the deflection from the equilibrium, and its direction is opposite to that of the deflection. Let us have a spring, for the deflection of which from the equilibrium position by r is necessary to exert the force F = -kr, where k is the spring stiffness. An equation of the motion of the harmonic oscillator, consisting of the spring and the weight with the mass m, is −kr = ma (as the application of the second Newton΄s law Σ F = ma), i.e.
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Physical Background
A semiconductor diode with PN junction (photovoltaic cell, resp. PV cell) is a well-known device.
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Physical Background
Heisenberg uncertainty principle states that the location and momentum of one arbitrary particle cannot be determined simultaneously with infinite accuracy. Let us consider a photon with the mass m and the momentum p.
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Physical Background
To study photoeletric effect we can choose one of these methods:
Method of charging capacitance on stopping voltage – simplier method.
Study of volt-amperove characteristics of vacuum phototube – more complex method, suitable for university stundets and students of technical subjects.
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Physical Background
In remote experiment we will observe statistical laws, ie. dependency of measured values on measuring time, respectively count of repeated measurements, dependency of radioactive measure on variable conditions, that is: distance from radioactive emitter, thickness of shielding material, type of shield. Radioactive measure is defined by count of events, which are detected by Geiger-Müller detector.
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Physical Background
In quantum physics some physical quantities describing objects in microworld (e.g. elementary particles) can't have arbitrary but only some allowed values in contrary to macroworld. In the introduction we mentioned quantization of electron energy in atomic orbital. Quantization effetcs angular momentum of electron, too, and many other quantities. In 1913, Niels Bohr used these ideas and derived relation for energy and angular momenturm of electronu in hydrogen atom. Probabilist interpretation of wavefunction can explain us, why are basic physical quantities quantized. Wavefunction is basic tool for description of object properties in microworld. We can't link wavefunction with some visual vlnovou funkci si těžko spojíme s nějakou názornou idea – one reason is it is a complex function. However, its absolute value (which is always real number) is proportional to probability of measuring certain allowed value of physical quantity (e.g. position, momentum, energy, and so on). In simple systems such as hydrogen atoms, the probabilty function should be continuous!
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The arrangement of the remote experiment Water level controlling is seen in Fig.1 and Fig.2. It is in fact the manual water level controller, consisting of vessel (1) and the pump (2) with the closed colourer water circuit and the detecting water level system. All is built by the building blocks of the system ISES (Internet School Experimental System (see……): the relay (3), which switches on and off the pump and the liquid level detector consisting of two probes (4), which measure the water level using ISES panel. The on-line Web Camera (5) scans the whole demonstration. The server software is compiled using the kit software ISES WEB Control. The user can control the water level interactively by clicking the controls of the control panel.
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Physical Background
A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The process is known as rectification. Physically, rectifiers take a number of forms, including vacuum tube diodes, mercury-arc valves, copper and selenium oxide rectifiers, semiconductor diodes, silicon-controlled rectifiers and other silicon-based semiconductor switches. Historically, even synchronous electromechanical switches and motors have been used. Early radio receivers, called crystal radios, used a "cat's whisker" of fine wire pressing on a crystal of galena (lead sulfide) to serve as a point-contact rectifier or "crystal detector". Rectifiers have many uses, but are often found serving as components of DC power supplies and high-voltage direct current power transmission systems. Rectification may serve in roles other than to generate direct current for use as a source of power. As noted, detectors of radio signals serve as rectifiers. In gas heating systems flame rectification is used to detect presence of a flame. Because of the alternating nature of the input AC sine wave, the process of rectification alone produces a DC current that, though unidirectional, consists of pulses of current. Many applications of rectifiers, such as power supplies for radio, television and computer equipment, require a steady constant DC current (as would be produced by a battery). In these applications the output of the rectifier is smoothed by an electronic filter (usually a capacitor) to produce a steady current.
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The series RLC circuit above has a single loop with the instantaneous current flowing through the loop being the same for each circuit element. Since the inductive and capacitive reactance’s XL and XC are a function of the supply frequency, the sinusoidal response of a series RLC circuit will therefore vary with frequency, ƒ. Then the individual voltage drops across each circuit element of R, L and C element will be “out-of-phase” with each other as defined by: i(t) = Imax sin(ωt) The instantaneous voltage across a pure resistor, VR is “in-phase” with the current. The instantaneous voltage across a pure inductor, VL “leads” the current by 90o The instantaneous voltage across a pure capacitor, VC “lags” the current by 90o Therefore, VL and VC are 180o “out-of-phase” and in opposition to each other.
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Electrons in atoms obey Pauli excluding principle – there are no two electrons with same sets of quantum numbers values. So the elcetrons sit on energy levels from the lowest one. At zero temperature (0 K), there is no energy level from the lowest one to the highest one, which would be not occupied.
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In this Millikan experiment different forces are acting on a charged oil droplet positioned in the homogenous field of a plate capacitor. By an indirect measurement via velocity measurements, one can determine these forces. To measure the charge Q of an electrically charged oil droplet by the Millikan experiment, one must consider two different movements of the droplet: in one case an upward motion under the influence of an electric field. In the other case a downward motion without an electric field. From the balance of forces during upward motion one can determine the charge of the oil droplet. To calculate this charge one must know the radius r of the respective spherical oil droplet; but this radius r can not be determined directly. Though r can be determined indirectly by considering the balance of forces during downward motion.
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With this technique one can generate 2-dimensional layer picture of objects without perturbing superpositions. Nowadays this technique has been improved such that one is able to generate quasi 3-dimensional pictures of the volume of a body. Besides this technique (CT) other similar techniques are magnetic resonance tomography (MRT), ultra sound tomography (UST), positron emission tomography (PET) and single-photon emission tomography (SPEC). All these techniques are different in their working principles as well as in their various medical applications. For example CT is used to display "hard" parts of a body like bones, whereas MRT is favored to display "soft" parts.
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Physical Background
In general the amount of an object (e.g. a moving car, sound propagation, expansion of a light pulse) moving with constant velocity v is defined as the difference in distance s divided by the passed time intervall t: v=s/t
As an example: If one is driving a car a distance s = 100 km from A to B in one hour, the avarage velocity of this car is 100 km/h = 28 m/s. For comparison sound is dispersing in air with a velocity of 340 m/s, whereas in water with 1500 m/s, light in vacuum approx. 300 000 000 m/s. The velocity of light c can be determined by this time of flight method measuring the interval Δs and the interval in time Δt.
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Physical Background
The oscilloscope is a basic tool to display periodic, time dependent voltages, which will be presented on its screen. There are two versions, analog and digital oscilloscopes. The incoming signal can be stored by a digital oscilloscope. By that technique, for example, very slow processes, which may happen only once, can be displayed.
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Physical Background
Since we know materials, which are conducting electric current (conductors) or not (isolators), semiconductors must be materials, which passes an electric conductivity between the former two ones. To model the different cases of electric conductivity - such as conductor, semiconductor, isolator - we use the energy band model, which requires a certain basic knowledge in solid state physics.
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If a body is moving relative to a gas or a liquid then a force is acting on that body, whose direction is opposite to the direction of motion. These force is called flow resistance, in case of air as flowing gas it is called air resistance. The reason for this flow resistance is different for laminar and turbulent flow. In case of laminar flow the internal friction of the medium causes this flow resistance.
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Physical Background
Due to the experimental situation we can make the following simplifications and approximations:
Coherent light is illuminating the diaphragm (i. e. constant phase differences between partial light waves and as consequence a stable diffraction pattern)
Monochromatic light of wavelength λ hits the diaphragm (i. e. constant amount k = 2π/λ of wave vector)
Distance s between diffracting object and diffraction pattern is large in comparison to dimensions of diffracting object (i. e. Fraunhofer condition for diffraction)
Diffraction angles are small (i. e. one can use sinα ≈ α for diffraction angles less than 5°).
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Physical Background
Let us assume that the double slit consists of two parallel slits of the same width b with the center spacing g. Each of the rays passing through one of the slits is subjected to diffraction as described in section 1. However, the interference of the two rays, which emerge from each of the two slits at the same angle, must now also be taken into consideration.
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We can explain this phenomenon, if we suppose that light behaves like a wave with wavelength λ. From each point within a slit of the diffracting object a circular wave starts and all these circular waves interfere behind the diffracting object. Instead of drawing all the wavefronts of all circular waves we pictured in Fig. 5 only the wave rays from the borders of the slits to an arbitrary choosen point P on the screen (see Fig. 4). The distance e = 1.005 m between diffracting object and screen is much larger than the 3 mm diffracting object. Therefore
the wave rays towards the observation point P are approximately parallel (Fraunhofer approximation) and we can work with one and the same diffraction angle α (-90° < α < 90°).
the diffraction angle α and the position x on the screen can be easily transformed into each other exactly or approximately for small angles measured in radian (|α| < π/36 ≡ 5°) by x = e tan α ≈ eα. For x ≥ 0 is α ≥ 0, for x < 0 is α < 0.
because of the small diffracted beam in the direction α we don´t need a lens to focus the beam on the screen.
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