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, October 1, 2011
SPECTRUM OF LIGHT
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WE all know that light is made up seven different colour which can be remember as VIBGYOR . and when the light passes from a prism, due to different wave length and different speed of different colour of light all colour bent to different extent and when they will come out from prism we will get a band of seven colour which is known as spectrum. and the phenomena due to which white light splits up into seven different colour is known as dispersion of light.
Now this spectrum which lie between red and violet which is visible to us is a very small portion og electromagnetic spectrum. experiments show that this spectrum does not end only on this visible spectrum but it lie beyond this spectrum and is not visible to us and this part of spectrum is known as invisible spectrum.the complete wave of electromagnetic radiation are given below in order of their increasing wavelength and decreasing frequency. is given below
gamma rays X rays Ultra violet ray visible light Infrared microwave radiowave
Now this spectrum which lie between red and violet which is visible to us is a very small portion og electromagnetic spectrum. experiments show that this spectrum does not end only on this visible spectrum but it lie beyond this spectrum and is not visible to us and this part of spectrum is known as invisible spectrum.the complete wave of electromagnetic radiation are given below in order of their increasing wavelength and decreasing frequency. is given below
gamma rays X rays Ultra violet ray visible light Infrared microwave radiowave
Tuesday, September 27, 2011
power of lens and magnification power of lens
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POWER OF LENS:We all know that what the main function of lense it is only either to converge or to diverge the rfay of light. So if the lens can converge or diverge the light more easily it means lens is more powerful. now we all know if the rays are coming from infinity they will converge at focus so if the lens is more powerful the the rays will converge very soon or u can say that the focus will be near to the lens or the lens is of small focal length. It means if the lens is of short focal length is is of more powerful. or power of the lens is inversely proportional to focal length of a lens. Means more the power of the lens less will be its focal length and hence vice a versa.
UNIT OF POWER : power of a lens is measured in Diopter.
if focal length of the lens is 1 m the the power of the lens is 1 diopter. so 1 diopter can be defined as the power of the lens whose focal length is 1 m.
power of convex lens is taken as positive and power of cancave lens is taken as negative the reason is that in convex lens rays are actually meet at focus so is has real focus but in concave lens reays are not actually meet at focus but the are appears to meet at focus so it has a virtual focus.
UNIT OF POWER : power of a lens is measured in Diopter.
power of convex lens is taken as positive and power of cancave lens is taken as negative the reason is that in convex lens rays are actually meet at focus so is has real focus but in concave lens reays are not actually meet at focus but the are appears to meet at focus so it has a virtual focus.
Wednesday, August 3, 2011
INCLINED PLANE AND ITS MECHANISM
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You must have seen a sloping surface at the entrance of your home, or in the automobile workshops which is used to lift the heavy objects on the higher place. And that sloping surface is known as inclined plane, so in easy language, we can define the inclined plane as a flat sloping surface which is used to lift heavy object on a higher place whose one end is attached to the ground and second end is attached with the higher surface.
MECHANICAL ADVANTAGE OF INCLINED PLANE :-
The mechanical advantage of inclined plane is always greater than one i.e . it is used to multiply the force. And mechanical advantage is inversely proportional to the angle of inclination. means more is the angle of inclination, lesser will be the mechanical advantage and lesser is the angle of inclination, more is the mechanical advantage.
Thats why, we will get more tired when we move on a steeper hill, than on less steeper hill, it means if we increase the length of the inclined plane, the mechanical advantage will be increase.
MAGNETIC FIELD
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Activities:
Take a bar magnet and place a steel pin at some distance Nothing happens. Now bring a steel pin near the pole of the bar magnet. It will stick to the magnet.
Activities:
Take a drawing board and fix a smooth white sheet of paper on it with the drawing pins. Sprinkle fine powder of iron filing on it such that it is spread evenly on paper. Now place a bar magnet in the middle of the white sheet. Tap the drawing board gently. The iron fillings move and re-position them- selves in the form of curves. This activity shows that magnetic substances experience a force by a magnet.
· The space around the magnet where its influence can be detected is called magnetic field. Take a drawing board and fix a white sheet of paper on it place a magnet on white sheet and draw its boundary. Now place a small compass needle close to the north pole of the magnet and mark two pencil dots exactly at the end of the needle. Mark the points one and two. Now lift the compass and place it in such a way that one end of the compass points towards the point two. Now mark the new end as three. Repeat it till 7 numbers etc. Join the points to get a continuous curve. Thus one magnetic line force is traced. Repeat the process from the north pole of the magnet from a different point and trace another magnetic line of force.
· Each line is a closed continuous curve
· They originate at the North Pole and terminate at the south pole of a magnet.
· The lines are crowded near the poles where magnetic lines are strong.
They do not intersect each other. Any source of magnetism such as a magnet or an electromagnet, is surrounded by a magnetic field. That field can be detected by various devices, which can also give information about the direction of the field and even its strength.
A simple compass can detect a magnetic field and demonstrate its direction. Iron filings can be used to show the shape of a magnetic field. At the sophisticated level, a gaussmeter can detect a field and indicate its strength, as measured in gauss units.
Compass: A compass is simply a thin magnet or magnetized iron needle balanced on a pivot. It can be used to detect small magnetic fields. The needle will rotate to point toward the opposite pole of a magnet. It can be very sensitive to small magnetic fields.
Using a compass to show the magnetic field:
When you bring a compass near an item suspected of being magnetized or having a magnetic field, the compass will turn and point toward the appropriate pole of the object.
A famous experiment showed that a wire with DC electric current running through it created a magnetic field. When the electricity was turned on, a nearby compass moved to indicate a magnetic field was present.
By spreading fine iron filings or dust on a piece of paper laid on top of a magnet, you can see the outline of the magnetic lines of force or the magnetic field.
Iron filings and compasses show the shape and direction of the magnetic field
This experiment also shows that magnetism will act through many materials, such as paper. Would the experiment work if a sheet of iron were used to sprinkle the filings? What about aluminum foil?
Gaussmeters are used to measure the strength of a magnetic field. They use an electronic chip called a Hall effect device, which gives off a tiny electrical current when exposed to a magnetic field. The current is amplified with electronic circuitry and a meter shows the number of gauss (the units of magnetic field strength). These devices are used to detect and measure magnetic fields in scientific experiments, in industry and even in people's homes.
Take a bar magnet and place a steel pin at some distance Nothing happens. Now bring a steel pin near the pole of the bar magnet. It will stick to the magnet.
Activities:
Take a drawing board and fix a smooth white sheet of paper on it with the drawing pins. Sprinkle fine powder of iron filing on it such that it is spread evenly on paper. Now place a bar magnet in the middle of the white sheet. Tap the drawing board gently. The iron fillings move and re-position them- selves in the form of curves. This activity shows that magnetic substances experience a force by a magnet.
· The space around the magnet where its influence can be detected is called magnetic field. Take a drawing board and fix a white sheet of paper on it place a magnet on white sheet and draw its boundary. Now place a small compass needle close to the north pole of the magnet and mark two pencil dots exactly at the end of the needle. Mark the points one and two. Now lift the compass and place it in such a way that one end of the compass points towards the point two. Now mark the new end as three. Repeat it till 7 numbers etc. Join the points to get a continuous curve. Thus one magnetic line force is traced. Repeat the process from the north pole of the magnet from a different point and trace another magnetic line of force.
· Each line is a closed continuous curve
· They originate at the North Pole and terminate at the south pole of a magnet.
· The lines are crowded near the poles where magnetic lines are strong.
They do not intersect each other. Any source of magnetism such as a magnet or an electromagnet, is surrounded by a magnetic field. That field can be detected by various devices, which can also give information about the direction of the field and even its strength.
A simple compass can detect a magnetic field and demonstrate its direction. Iron filings can be used to show the shape of a magnetic field. At the sophisticated level, a gaussmeter can detect a field and indicate its strength, as measured in gauss units.
Compass: A compass is simply a thin magnet or magnetized iron needle balanced on a pivot. It can be used to detect small magnetic fields. The needle will rotate to point toward the opposite pole of a magnet. It can be very sensitive to small magnetic fields.
Using a compass to show the magnetic field:
When you bring a compass near an item suspected of being magnetized or having a magnetic field, the compass will turn and point toward the appropriate pole of the object.
A famous experiment showed that a wire with DC electric current running through it created a magnetic field. When the electricity was turned on, a nearby compass moved to indicate a magnetic field was present.
By spreading fine iron filings or dust on a piece of paper laid on top of a magnet, you can see the outline of the magnetic lines of force or the magnetic field.
Iron filings and compasses show the shape and direction of the magnetic field
This experiment also shows that magnetism will act through many materials, such as paper. Would the experiment work if a sheet of iron were used to sprinkle the filings? What about aluminum foil?
Gaussmeters are used to measure the strength of a magnetic field. They use an electronic chip called a Hall effect device, which gives off a tiny electrical current when exposed to a magnetic field. The current is amplified with electronic circuitry and a meter shows the number of gauss (the units of magnetic field strength). These devices are used to detect and measure magnetic fields in scientific experiments, in industry and even in people's homes.
Monday, January 17, 2011
LOCOMOTION IN ANIMALS
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Locomotion in animals is common, - organs which help in movement in common animals like - Mammals, insects, birds, fish, earthworm- Different kinds of movements, Movement in human beings- Muscles, joints, ligaments, tendons, cartilage joints in human body- different kinds of joints; Muscles work in pairs to produce movement , Difference between movement and lococmotion, movement in plants- phototropism, geotropism, hydrotropism- Positive and negative responses to the stimuli, Thigmotropism, Tropic and nastic movements, Movement of microscopic living things- Amoeba, paramecium, Euglena
Cranium - the part of skeleton that encloses the brain
Geotropism - movement of plant parts in response to force of gravity
Hydrotropism- movement of plant parts in response to moisture
Nastic movements- nondirectional plant movements in response to environmental stimuli
Phototropism- movement of plant parts in response to light
Skeleton - the hard framework that supports the body
Thigmotroprism- growth in response to touch
Tropic movements- directional plant movements in response to some environmental stimuli where direction of movement is determined by the direction of stimulus.
Friday, January 14, 2011
IMPEDANCE MATCHING
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By the matching of impedances we understand a selection of impedances between different media in such a way tha maximum transfer of energy takes place from one medium to the other. This is essential requirement in many practical situations. Thus, impedance matching represents a very important practical problem via -a - vis energy transfer
My dear friends, here today i will tell some good about this topic,
By the matching of impedances we understand a selection of impedances between different media in such a way tha maximum transfer of energy takes place from one medium to the other. This is essential requirement in many practical situations. Thus, impedance matching represents a very important practical problem via -a - vis energy transfer
i) Long distance cables - carrying energy have many lengths of wire joined end to end. These cables must be accurately matched at all joints, so that there is no wastage from energy reflection.
ii) A loudspeaker - has to be matched to the impedance of the power output of an amplifier by choosing the correct turns ratio on the coupling transformer. The amplifier gives us am amplified signal of the input signal (voice, music)
iii) The power transfer from a generator to ta circuit or electrical network is a maximum when the generator impedance is carefully matched with the circuit load.
The insertion of a coupling element between two mismatched impedances is of fundamental importance. It finds applications in many branches of physics, engineering. Such systems also exist in optics. We describe the physics of impedance matching by taking the case of mechanical waves on a string, but the results can be taken as valid for all kinds of waves.
We know that at a joint of two different impedances, there is a definite reflection of incident energy of the wave. Such impedances are called mismatching.
Monday, January 10, 2011
ATMOSPHERE AND ITS LAYERS
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1. Troposphere - This layer is extended upto 8 to 14 kms from the surface of the earth. This layer act as a medium for growth for plants and animals, all living things live on this layer, all plants grow on this layer, This layer become turbulent due to different temperature changes, all the season changes in this layer.
Atmosphere and its layers - We live on earth and there is air around us, and this blanket of air around us is known as atmosphere, Atmosphere is extended upto 800 kms from the surface of the earth. The air near the earth surface is denser and as we go higher and higher, its density decreases and it become thinner and thinner. Atmosphere mainly have five layers.
1. Troposphere - This layer is extended upto 8 to 14 kms from the surface of the earth. This layer act as a medium for growth for plants and animals, all living things live on this layer, all plants grow on this layer, This layer become turbulent due to different temperature changes, all the season changes in this layer. 2. Stratosphere - This layer extended upto 50 kms from the surface of the earth. It provide good atmosphere for aeroplanes and helicoptors. Ozone layer is also present in this layer, this ozone layer protects us from harmful UV radiations coming from the sun, if this radiation reaches on earth, the people will suffer from skin cancer.
3. Mesosphere -- This layer extended upto 85 kms from the surface of the earth. In this layer all the heavenly bodies like stars, comets are present, very big rocks which are known as meteoroid are present in this layer, When this big burning rocks also knows as shooting stars enter in this layer, there layers reduces them in their size.
4. Ionosphere - This layer is also known as thermosphere, and is extended upto 640 kms from the surface of the earth, so, just because of excessive heat in it, as the sun heat this layer upto 1500 degree celcius, This layer also having atoms and molecules, due to heat of sun, these atoms and molecules get ionized and releases ions.
5. Exosphere - This layer is extended upto 800 kms from the surface of the earth. This layer is external layer
Sunday, January 9, 2011
VELOCITIES ASSOCIATE WITH WAVELENGTH
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Often we come across different types of velocities, associated with wave motion, in one way or the other. For instance, we talk about the 1) particle -velocity, 2) wave velocity or phase -velocity and group velocity. Each has got a distinct definition as well as physical meaning for it. Before we proceed to discuss different types of velocities, it is worthwhile to bear in mind that a wave motion is a collective response of a large number of oscillators through which the disturbance goes, one by one,. Also, each of these oscillators undergoes a simple harmonic motion (S.H.M), at its own location. The very important fact here is that these individual oscillators of the medium, through which the wave progresses / advances, do not progress move along with the traveling wave. The motion of these oscillators about their mean positions can be transverse or longitudinal. What we observe as a wave motion is the locus of different particle phases. In other words, the waves as observed by us are the phase relationships of different particle oscillators coupled and not their progressive motion through the medium they constitute.
Often we come across different types of velocities, associated with wave motion, in one way or the other. For instance, we talk about the 1) particle -velocity, 2) wave velocity or phase -velocity and group velocity. Each has got a distinct definition as well as physical meaning for it. Before we proceed to discuss different types of velocities, it is worthwhile to bear in mind that a wave motion is a collective response of a large number of oscillators through which the disturbance goes, one by one,. Also, each of these oscillators undergoes a simple harmonic motion (S.H.M), at its own location. The very important fact here is that these individual oscillators of the medium, through which the wave progresses / advances, do not progress move along with the traveling wave. The motion of these oscillators about their mean positions can be transverse or longitudinal. What we observe as a wave motion is the locus of different particle phases. In other words, the waves as observed by us are the phase relationships of different particle oscillators coupled and not their progressive motion through the medium they constitute. 1) The Particle velocity - It is simply the velocity with which the simple harmonic oscillator moves about its mean or equilibrium position. As already discussed, this motion can be transverse or longitudinal direction of wave motion.
2) The wave velocity or Phase velocity - As we all know, crests and troughs represent planes of equal phase. the wave or phase velocity has been defined as the velocity with which planes of constant phase advance through the given medium.
3) The group velocity- It is an established fact that waves rarely occur/exist as single monochromatic components. Instead that , what we have is a superposition of a number of waves of different characteristics. The resulting composite entity is called a wave group.
Saturday, January 8, 2011
TYPES OF WAVES
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Well, one of the easiest and simplest ways to demonstrate the formation of waves is to hold the loose end of a rope which is fixed at the other end and to move it quickly up and down. Crests and troughs of the waves advance towards the fixed end of the rope. If the rope is very long, we can observe such a crest or trough. For the formation of progressive waves, we have a long unlimited rope , but if the medium is limited, of finite extent as we have in the case of a violin having a small string, fixed at both in ends, an interesting thing happens.
The progressive waves traveling on the string will get reflected at both fixed ends. Due to the superposition of incoming and reflected waves along the string results in the formation of standing waves. Standing waves or stationary waves are therefore formed /produced by the simultaneous transmission of two identical wave motions in opposite directions. Remember, we are talking about the mechanical waves. EM- waves like radio-waves, X-rays, light waves etc. are a class of their own and can travel even without a material medium. Mechanical waves are of two types:-
1) Transverse waves - are the waves in which the vibration of displacement takes place in a plane at right angles to the direction of propagation of the wave. Even non -mechanical waves are transverse in character. Waves on a stretched string are of this type only, as also the waves produced in a string.
2) Longitudinal waves- are the waves in which the vibration or displacement take place in the direction of propagation of the waves, sound waves and waves in a long spring the free end of which is pulled or pushed along its length fall in this category.
ELECTRICAL OSCILLATOR
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Before begin with, suppose the capacitor is fully charged, with magnitude of charge q0 on each plate, with the help of the battery B AND key K. Now breaking the battery ckt, the charged capacitor is connected across the inductor through the other key K. The capacitor will begin to discharge through the coil. The flow of charge from C through L constitutes a current I. This changing current sets up a magnetic field around the coil L. Soon, a stage comes when C is fully discharged and the field around L is saturated. The variations of magnetic field in the coil give rise to self induced emf which according to Lenz's law is with polarity opposite to that on the capacitor plates a little while ago.This back end recharges the neutral capacitor, plates acquire charge in opposite sense now. In the absence of resistance in this ckt., the energy of the electrical system remains constant and is exchanged between the MAGNETIC field energy stored in the coil and the ELECTRIC field energy stored between the plates of the capacitor.
Again, the process of discharging begins through the coil but the direction of current is reversed. A magnetic field is again set up around the coil, but with opposite polarity, till it reaches a saturation point and the capacitor is fully discharged The variations of magnetic flux again set up an induced emf in the coil. The induced current then recharges the capacitor to the saturation level of charge on its plates, and we regain the original starting stage.
Again, the process of discharging begins through the coil but the direction of current is reversed. A magnetic field is again set up around the coil, but with opposite polarity, till it reaches a saturation point and the capacitor is fully discharged The variations of magnetic flux again set up an induced emf in the coil. The induced current then recharges the capacitor to the saturation level of charge on its plates, and we regain the original starting stage.
Friday, January 7, 2011
ROLE OF ELASTICITY AND INERTIA SUMMARY
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c) A mass (m) attached to the free end of a fixed spring moving back and forth on a frictionless floor.
A small displacement from its equilibrium position sets up a restoring force, this force is proportional and acts in such a direction towards the equilibrium position.
Dear, now let us again take a closer look at some of the physical systems in motion ;
a) A simple pendulum with a swinging mass m at the end of a fixed light string of length l.
b) a torsional pendulum disc supported by and swinging about the same suspension wire/string.
c) A mass (m) attached to the free end of a fixed spring moving back and forth on a frictionless floor. d) A liquid column moving up and down a U-tube of uniform corss-sectional area about its equilibrium position of equal levels in each limb.
e) An electrical circuit having an inductance L across a capacitance C carrying a charge q.
So, mechanical as well as Electrical systems are now equivalent in their treatment.
A small displacement from its equilibrium position sets up a restoring force, this force is proportional and acts in such a direction towards the equilibrium position.
The equilibrium or rest position is equivalent to the mean position of a SHO
These observations are very vital to the understanding of the mechanism of S.H.M.
So, this restoring force is because of elasticity of the given medium. The disturbed system tries to recover and restore its original position after the deforming force is removed. The inertia of the medium comes into the picture now. Because of this property, the motion is repeated on either side of the mean position. In the absence of elasticity the recovery from the disturbed position of the given medium is not possible. And without inertia the undulations are not repeated. Thus we come on conclusion , that elasticity and inertia are two essential properties of a medium to sustain any harmonic wave motion.
Tuesday, January 4, 2011
SIMPLE HARMONIC MOTION IN PHYSICS
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Dear, before we take any detailed study of SIMPLE HARMONIC MOTION, let understand first the meaning of the word 'motion' and harmonicity or periodicity of a motion. So we see different objects around us, we generally call some of them moving, while others are at rest if an object does not change its position with the passage of that time, it is at rest. But if the position vector of a body changes with time, it is surely in the state of motion. Rest and motion, as all of us know are only relative concepts.
No object in this world can ever be in a absolute motion or at absolute rest. An object can have three types of motion :-
1 Translatory Motion- is the motion in which the object advances along a straight path, from point to point, as the time is elapsed or along a smooth curvillinear path.
2. Rotatory Motion - involves the motion of an object about a fixed point, often repeatedly covering the same path. Such a motion may be uniform or non-uniform.
3. Vibratory motion- is a motion, a body is found to move back and forth, on a given stretch of path, about a fixed point called its mean position.
While in case 1, the path is never repeated as the body advances, in cases 2 and 3 it is not so, The body repeats its motion on along the same fixed track. Typical eg. can be enumerated for each type of motion. For instance , a freely falling object an object sliding down an inclined plane, a train running over its track etc. are examples of translatory motion, Motion of our own earth around the sun, hands of a clock, an electron moving around an atomic nucleus, etc are typical eg. of rotatory motion. Motion of a clock pendulum, fluttering wings of a honey bee etc. are all eg. of vibratory motion.
No object in this world can ever be in a absolute motion or at absolute rest. An object can have three types of motion :-
1 Translatory Motion- is the motion in which the object advances along a straight path, from point to point, as the time is elapsed or along a smooth curvillinear path.
2. Rotatory Motion - involves the motion of an object about a fixed point, often repeatedly covering the same path. Such a motion may be uniform or non-uniform.
3. Vibratory motion- is a motion, a body is found to move back and forth, on a given stretch of path, about a fixed point called its mean position.
While in case 1, the path is never repeated as the body advances, in cases 2 and 3 it is not so, The body repeats its motion on along the same fixed track. Typical eg. can be enumerated for each type of motion. For instance , a freely falling object an object sliding down an inclined plane, a train running over its track etc. are examples of translatory motion, Motion of our own earth around the sun, hands of a clock, an electron moving around an atomic nucleus, etc are typical eg. of rotatory motion. Motion of a clock pendulum, fluttering wings of a honey bee etc. are all eg. of vibratory motion.
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.
Tuesday, November 30, 2010
ACID AND ITS CLASSIFICATION
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ACID: Acids are the substance which when dissolve in water give hydrogen ion or hydronium ion .
Acids are classified into two category on the basis of their occurrence:
Organic acid : the acids which obtained from the nature and in living things and plants called organic acid.For Example vinegar, citric acid in lemon.
Inorganic acid: the acids which are obtained from the minerals of earth crust called inorganic acid.for Example sulphuric acic, hyrochloric acid.
on the basis of their strength:
Weak acid: The acid which do not dissociate completely when dissolve in water. for example acetic acid
Strong Acid: The acid which completely dissociate in dissolve in water and give more concentration on hydrogen ion. For example hydrochloric acid.
on the basis of their concentration:
Concentrated Acid: chemical in which more amount of acid less amount of water.
Weak acid : Chemical in which less amount of acid and more amount of water
on the basis of their basicity:
Monobasic acid: the acis which give only one hyrogen ion when dissociate in water example hydrochloric acid
Diabasic Acid: The acid which give two hydrogen ion when dissolve in water for example sulphuric acid
Tribasic Acid: The acid which give three hydrogen ion when dissolve in water for example phosphoric acid.
ACID: Acids are the substance which when dissolve in water give hydrogen ion or hydronium ion .
Acids are classified into two category on the basis of their occurrence:
Organic acid : the acids which obtained from the nature and in living things and plants called organic acid.For Example vinegar, citric acid in lemon.
Inorganic acid: the acids which are obtained from the minerals of earth crust called inorganic acid.for Example sulphuric acic, hyrochloric acid.on the basis of their strength:
Weak acid: The acid which do not dissociate completely when dissolve in water. for example acetic acid
Strong Acid: The acid which completely dissociate in dissolve in water and give more concentration on hydrogen ion. For example hydrochloric acid.
on the basis of their concentration:
Concentrated Acid: chemical in which more amount of acid less amount of water.
Weak acid : Chemical in which less amount of acid and more amount of water
on the basis of their basicity:
Monobasic acid: the acis which give only one hyrogen ion when dissociate in water example hydrochloric acid
Diabasic Acid: The acid which give two hydrogen ion when dissolve in water for example sulphuric acid
Tribasic Acid: The acid which give three hydrogen ion when dissolve in water for example phosphoric acid.
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