A mosquito repellent is a substance applied to skin, clothing, or other surfaces which discourages mosquitoes (and arthropods in general) from landing or climbing on that surface. There is also Mosquito repellent products available based on sound production, particularly ultrasound (inaudibly high frequency sounds). These electronic devices have been shown to have no effect as a mosquito repellent by studies done by the EPA and many universities.
A liquid Mosquito repellent is a kind of a liquid which is applied to skin which helps to discourage mosquitoes. liquid mosquito repellents help prevent and control the outbreak of Mosquito-borne diseases such as malaria, Lyme disease, Dengue fever, bubonic plague, and West Nile fever. Pest animals commonly serving as vectors for disease include the mosquito’s flea, fly, and mosquito; and the arachnid tick.
Saturday, December 11, 2010
FRAUNHOFFER DIFFRACTION
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Ok, Dear we now consider fraunhoffer diffraction of monochromatic light by a narrow slit. Let a parallel beam of monochromatic light be incident normally on an opaque plate having a long narrow slit in it.
According to geometrical optics, the transmitted beam, on the screen, should have uniform illumination of the same cross-section (X,Y) as that of the slit. Contrary to this, when a transmitted beam is focused by a lens on the screen, we observe a diffraction pattern. It consists of
(i) A very intense central bright band, much wider than the slit width, in the direction of incidence.
ii) A set of dark and subsidary maxima of decreasing intensity, on either side of central bright band.
iii) The central bright maxima is called Central Maxima and secondary Maxima.
To obtain a Fraunhoffer class of diffraction due to a slit, the incident wavefront is plane which is obtained by using a convex lens in such a way that source lies in the focal plane of the lens. The diffracted light from the slit is again collected on the screen with the help of convex lens, so that the source and screen are at infinite distances from the obstacle. The experimental arrangement is a source of monochromatic light of wavelength.
Ok, Dear we now consider fraunhoffer diffraction of monochromatic light by a narrow slit. Let a parallel beam of monochromatic light be incident normally on an opaque plate having a long narrow slit in it.
According to geometrical optics, the transmitted beam, on the screen, should have uniform illumination of the same cross-section (X,Y) as that of the slit. Contrary to this, when a transmitted beam is focused by a lens on the screen, we observe a diffraction pattern. It consists of
(i) A very intense central bright band, much wider than the slit width, in the direction of incidence.
ii) A set of dark and subsidary maxima of decreasing intensity, on either side of central bright band.
iii) The central bright maxima is called Central Maxima and secondary Maxima.
To obtain a Fraunhoffer class of diffraction due to a slit, the incident wavefront is plane which is obtained by using a convex lens in such a way that source lies in the focal plane of the lens. The diffracted light from the slit is again collected on the screen with the help of convex lens, so that the source and screen are at infinite distances from the obstacle. The experimental arrangement is a source of monochromatic light of wavelength.
Tuesday, December 7, 2010
METHOD OF REDUCING SPHERICAL ABERRATION
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Dear readers, here is me with new topic regarding physic science about method of reducing spherical aberration as follow:
The spherical aberration as explained above cannot be eliminated completely for a single lens with spherical surfaces. This is because it arises due to the 'spherical' shape of the lens and its amount is proportional to the square of the radius of the portion of lens surface through which the light rays pass. It can, however, he reduced appreciably by the following methods :
i) By use of stops. Obviously spherical aberration can be reduced it either the marginal rays or the central rays are cut off by using suitable stops, the rest of the rays come practically to a point focus. The stop is usually circular and its center coincides with the pole of the lens.In camera lenses the marginal rays are cut off by placing a narrow circular aperture. In telescope objectives, which have large aperture, the central rays are cut off by covering the central portion of the lens. But use of stops reduces the intensity of light and the brightness of the image.
ii) By combining suitable convex and concave lenses. We have already seen that the spherical aberration for a converging lens is positive and that for a diverging lens is negative. Therefore, by suitably combining a convex lens with a concave lens, spherical aberration may be minimized.
Dear readers, here is me with new topic regarding physic science about method of reducing spherical aberration as follow:
i) By use of stops. Obviously spherical aberration can be reduced it either the marginal rays or the central rays are cut off by using suitable stops, the rest of the rays come practically to a point focus. The stop is usually circular and its center coincides with the pole of the lens.In camera lenses the marginal rays are cut off by placing a narrow circular aperture. In telescope objectives, which have large aperture, the central rays are cut off by covering the central portion of the lens. But use of stops reduces the intensity of light and the brightness of the image.
ii) By combining suitable convex and concave lenses. We have already seen that the spherical aberration for a converging lens is positive and that for a diverging lens is negative. Therefore, by suitably combining a convex lens with a concave lens, spherical aberration may be minimized.
PRODUCTION OF POLARIZED LIGHT
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In this section we will study various methods for the production of linearly polarized light waves. The wire grid polarizer and the polaroid. A wire grid polarizer consists of a large number of thin copper wires placed parallel to each other. when an unpolarized light wave which is of course an electromagneic wave is incident on it, then the component of electric vector parallel to the length of wire is absorbed. This is because of the fact that the electric field does not work on the electrons inside the thin wires and the energy associated with the electric field is lost in the joule heating of the wires. On the other hand, as the wires are assumed to be very thin, the component of electric vector along x-axis passes through without much alternation. Thus, the emergent beam is linearly polarized with electric vector along the x-axis. However, for the system to be effective (i.e for the Ev component to be almost completely atteunated, the spacing between the wires should be clearly, the fabrication for such a polarizer for a 3 cm micro wave is relatively easy because the space has to be ~3cm. on the other hand, as the light waves are associated with a very small wavelength
Monday, December 6, 2010
NATURE OF LIGHT WAVES
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The experiments illustrating interference and diffraction of light studied in previous chapters have shown beyond doubt that light like sound is some form of wave motion. These experiments do not reveal whether the light waves are longitudinal or transverse because phenomenon of interference and diffraction can occur with both longitudinal and transverse waves. We shall, therefore, investigate the nature of light waves and to begin with, we shall describe an important feature which distinguishes the two types. From the study of sound, we know that sound travesl in the form of longitudial waves and properties of such a wave motion are the same with respect to any plane through its line of propagation while a transervese wave behaves differently in different planes. The statement can be illustrated by a simple mechanical analogy given below :
The experiments illustrating interference and diffraction of light studied in previous chapters have shown beyond doubt that light like sound is some form of wave motion. These experiments do not reveal whether the light waves are longitudinal or transverse because phenomenon of interference and diffraction can occur with both longitudinal and transverse waves. We shall, therefore, investigate the nature of light waves and to begin with, we shall describe an important feature which distinguishes the two types. From the study of sound, we know that sound travesl in the form of longitudial waves and properties of such a wave motion are the same with respect to any plane through its line of propagation while a transervese wave behaves differently in different planes. The statement can be illustrated by a simple mechanical analogy given below :Take a stretched rubber cord CD threading through two narrow slits S1 and S2 cut in card board pieces and placed parallel to each other in the vertical planes. End D of the cord is fixed. Now set up a longitudinal wave in CD by moving the end C forward and backward along the cord. Rotate any of the slits about CD as axis. It will be found that this rotation does not effect the passage of the wave, ie. the wave passes through the first and second slits without being affected at all i whatever position the slits may be arranged. Thus, a longitudinal wave motion has the same properties with respect to all planes throughout its line of advance.
MOSQUITO REPLELLANT
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Introduction
History:
The first truly effective active ingredient used in liquid mosquito repellents was citronella oil. This material is an herbal extract derived from the citronella plant, an Asian grass. While citronella had been used for centuries for medicinal purposes, its repellence was only accidentally discovered in 1901, when it was used as a hairdressing fragrance. Since citronella oil is a fragrant material, it is thought that the chemical terpenes of which it is composed are responsible for its repellent activity. Citronella oil does repel mosquitoes, but it has certain characteristics which limit its effectiveness. For example, it is very volatile and evaporates too quickly from surfaces to which it is applied. Also, large amounts are needed to be effective.
Mosquito repellent safety:
Regarding safety with Mosquito repellent use on children and pregnant women:
• Children may be at greater risk for adverse reactions to repellents, in part, because their exposure may be greater.
• Keep repellents out of the reach of children.
• Do not allow children to apply repellents to them.
• Use only small amounts of repellent on children.
• Do not apply repellents to the hands of young children because this may result in accidental eye contact or ingestion.
• Try to reduce the use of repellents by dressing children in long sleeves and long pants tucked into boots or socks whenever possible. Use netting over strollers, playpens, etc.
• As with chemical exposures in general, pregnant women should take care to avoid exposures to repellents when practical, as the fetus may be vulnerable.
Regardless of which repellent product used, it is recommended to read the label before use and carefully follow directions.[13] Usage instructions for repellents vary from country to country. Some Liquid mosquito repellents are not recommended for use on younger children.
Liquid Mosquito repellent is the most effective way to combat mosquitoes that may spread diseases such as malaria, dengue and Japanese encephalitis. Liquid liquid mosquito repellents with deep reach action keeps mosquito away from every corner of the home. They also keep the fresh with their unique fragrance.
Mosquito repellent safety:
Regarding safety with Mosquito repellent use on children and pregnant women:
• Children may be at greater risk for adverse reactions to repellents, in part, because their exposure may be greater.
• Keep repellents out of the reach of children.
• Do not allow children to apply repellents to them.
• Use only small amounts of repellent on children.
• Do not apply repellents to the hands of young children because this may result in accidental eye contact or ingestion.
• Try to reduce the use of repellents by dressing children in long sleeves and long pants tucked into boots or socks whenever possible. Use netting over strollers, playpens, etc.
• As with chemical exposures in general, pregnant women should take care to avoid exposures to repellents when practical, as the fetus may be vulnerable.
Regardless of which repellent product used, it is recommended to read the label before use and carefully follow directions.[13] Usage instructions for repellents vary from country to country. Some Liquid mosquito repellents are not recommended for use on younger children.
Liquid Mosquito repellent is the most effective way to combat mosquitoes that may spread diseases such as malaria, dengue and Japanese encephalitis. Liquid liquid mosquito repellents with deep reach action keeps mosquito away from every corner of the home. They also keep the fresh with their unique fragrance.
Sunday, December 5, 2010
MULTI BEAM INTERFEROMETRY -TOPIC
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The interference between two beams which are derived from a single beam either by division of wavefront or by division of amplitude. Here we shall discuss the interference due to many beams which are derived from a single beam by multiple reflections - division of amplitude.
If a plane wave falls on parallel glass plate, then the beam would undergo multiple reflections at the two surfaces and a large number of beams of decreasing amplitudes will emerge on both sides of the plate. These beams on either side interfere to produce interference pattern at infinity. The interference fringes so produced are much sharper than those formed by interference produced by two beams. The interferometers involving multiple beam interference have very high resolving power and have application in high resolution spectroscopy.
FABRY- PEROT INTERFEROMETER
Fabry -Perot interferometer is based on the principle of multiple beam interference. It consists of two plane parallel glass plates A and B whose inside surfaces are silvered. Light from a point S of an extended source falls on plate A at an angle 0. The transmitted light after multiple reflection between the glass plates in the air film is brought to focus at P by the lens L. The intensity of transmitted light is maximum when the path difference between the rays. The interference pattern is concentric rings with O as center. Each ring corresponds to a particular value of 0. The radius of the ring is OP and the fringes are called fringes of constant inclination or Haidinger Fringes.
INTERFERENCE OF LIGHT
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According to the wave theory of light, the light emitted from a source travels in the medium in the form of waves. With a single source of light, the distribution of light energy in the surrounding medium is uniform. When there are two sources, under certain conditions called coherent sources, the distribution of light energy is no longer uniform. There are certain regions where the intensity of light is maximum and there are also certain regions where the intensity of light is minimum. The energy due to the two sources is thus disturbed. This redistribution of light energy obtained by the superposition of light waves from two coherent sources of light is called interference of light. At points where the crest of one wave falls over the crest of the other wave or a trough of one wave falls over the trough of the other wave, the resultant amplitude of the resulting wave is maximum.
At such points the intensity of light is maximum and this is called constructive interference. Similarly at points where the crest of one wave falls over the trough of the other wave, the resultant amplitude of the resulting wave is minimum. At such point, the intensity of light is minimum and this is called destructive interference.
Types of Interference
Interference can be divided in the following two classes ;
a) Interference by division of wavefront: In this class, a wave-front is divided into two parts either by reflection or by refraction. These two parts obtained fro the same wavefront travel and interfere to produce interference pattern.
b) Interference by division of amplitude : In this class, the amplitude of beam of monochromatic light is divided into two parts either by partial reflection or refraction. The divided beams so obtained interfere and produce interference pattern.
According to the wave theory of light, the light emitted from a source travels in the medium in the form of waves. With a single source of light, the distribution of light energy in the surrounding medium is uniform. When there are two sources, under certain conditions called coherent sources, the distribution of light energy is no longer uniform. There are certain regions where the intensity of light is maximum and there are also certain regions where the intensity of light is minimum. The energy due to the two sources is thus disturbed. This redistribution of light energy obtained by the superposition of light waves from two coherent sources of light is called interference of light. At points where the crest of one wave falls over the crest of the other wave or a trough of one wave falls over the trough of the other wave, the resultant amplitude of the resulting wave is maximum.At such points the intensity of light is maximum and this is called constructive interference. Similarly at points where the crest of one wave falls over the trough of the other wave, the resultant amplitude of the resulting wave is minimum. At such point, the intensity of light is minimum and this is called destructive interference.
Types of Interference
Interference can be divided in the following two classes ;
a) Interference by division of wavefront: In this class, a wave-front is divided into two parts either by reflection or by refraction. These two parts obtained fro the same wavefront travel and interfere to produce interference pattern.
b) Interference by division of amplitude : In this class, the amplitude of beam of monochromatic light is divided into two parts either by partial reflection or refraction. The divided beams so obtained interfere and produce interference pattern.
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