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41. Method of determination of substance concentration. Method of the caliber graph, method of comparison.

Quantitative absorption analysis per any impurity in the solution usually based on two methods:

1. The method of calibration curve.

2. The method of comparison.

1. Method of calibration graph.

Prepare series of solutions with known concentration and measuring their absorbance. From the data obtained a calibration curve by plotting the OY axis of the optical density at 0X are the corresponding conc. Then, the absorbance of the test solutions and their conc. are scheduled. This method also serves as a test of the law of Burger-Lambert.

2. The method of comparison.

Measure the optical density of the solution of unknown concentration and standard solution. For the same thickness of the absorbent layer (dж=dct ) and the same wavelength. Applying the basic law of light absorption we obtain: Dx/Cx=D0/C0

42. Polarization of light by bio-systems. Light natural and polarized.

A light wave is an electromagnetic wave that travels through the vacuum of outer space. Light waves are produced by vibrating electric charges. A light wave that is vibrating in more than one plane is referred to as unpolarized light. Light emitted by the sun, by a lamp in the classroom, or by a candle flame is unpolarized light. Such light waves are created by electric charges that vibrate in a variety of directions, thus creating an electromagnetic wave that vibrates in a variety of directions. This concept of unpolarized light is rather difficult to visualize. In general, it is helpful to picture unpolarized light as a wave that has an average of half its vibrations in a horizontal plane and half of its vibrations in a vertical plane.

It is possible to transform unpolarized light into polarized light. Light whose electric field oscillates in a particular way is said to be polarized. If the oscillation is in a plane, the light is said to be plane polarized (top right). Plane polarized light can be polarized in different directions. Light can also be circularly polarized, with its electric field direction spiraling in a screw pattern. Circularly polarized light can be right-or left-handed (bottom). Light can consist of a combination of plane and circular polarization as well; its electric field spirals in a screw fashion with an elliptical cross-section. Such light is called elliptically polarized. Process of transforming unpolarized light into polarized light is known as polarization. There are a variety of methods of polarizing light. The four methods discussed on this page are: Polarization by Transmission, by Reflection, by Refraction, by Scattering. The most common method of polarization involves the use of a Polaroid filter. Polaroid filters are made of a special material that is capable of blocking one of the two planes of vibration of an electromagnetic wave. Polaroid serves as a device that filters out one-half of the vibrations upon transmission of the light through the filter. When unpolarized light is transmitted through a Polaroid filter, it emerges with one-half the intensity and with vibrations in a single plane; it emerges as polarized light. Polarization has a wealth of other applications besides their use in glare-reducing sunglasses. In industry, Polaroid filters are used to perform stress analysis tests on transparent plastics. As light passes through a plastic, each color of visible light is polarized with its own orientation. If such a plastic is placed between two polarizing plates, a colorful pattern is revealed.

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