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PROPERTIES OF SOUND

Sound is a sequence of waves of pressure which propagates through compressible media such as air or water. (Sound can propagate through solids as well, but there are additional modes of propagation). During their propagation, waves can be reflected, refracted, or attenuated by the medium.

The propagation is also affected by the motion of the medium itself. For example, sound moving through wind. Independent of the motion of sound through the medium, if the medium is moving, the sound is further transported.

Sound is transmitted through gases, plasma, and liquids as longitudinal waves, also called compression waves. Through solids, however, it can be transmitted as both longitudinal waves and transverse waves.

Pitch represents the perceived fundamental frequency of a sound.It is one of the major auditory attributes of musical tones along with duration, loudness, timbre, and sound source location.

 In audio signal processing and acoustics, an echo (plural echoes) is a reflection of sound, arriving at the listener some time after the direct sound

source:http://en.wikipedia.org/wiki/Intensity_(physics)

I THINK NOW I CAN POST REGULARLY........................

hi
to all
Sorry for not being on the blog for so many days ..........................

NEW IDEAS

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basic atomicstructure

Atoms are made up of 3 types of particles electrons , protons  and neutrons .  These particles have different properties.  Electrons are tiny, very light particles that have a negative electrical charge (-). Protons are much larger and heavier than electrons and have the opposite charge, protons have a positive charge.  Neutrons are large and heavy like protons, however neutrons have no electrical charge.  Each atom is made up of a combination of these particles.  Let's look at one type of atom:
 

A neutron walked into a bar and  asked how much for a drink.  The bartender replied,  "for you, no charge." -Jaime - Internet Chemistry Jokes

The atom above, made up of one proton and one electron, is called hydrogen (the abbreviation for hydrogen is H).  The proton and electron stay together because just like two magnets, the opposite electrical charges attract each other.  What keeps the two from crashing into each other?  The particles in an atom are not still.  The electron is constantly spinning around the center of the atom (called the nucleus).  The centrigugal force of the spinning electron keeps the two particles from coming into contact with each other much as the earth's rotation keeps it from plunging into the sun.  Taking this into consideration, an atom of hydrogen would look like this:
A Hydrogen Atom
Keep in mind that atoms are extremely small.  One hydrogen atom, for example, is approximately 5 x 10^-8 mm in diameter.  To put that in perspective, this dash - is approximately 1 mm in length, therefore it would take almost 20 million hydrogen atoms to make a line as long as the dash.  In the sub-atomic world, things often behave a bit strangely.  First of all, the electron actually spins very far from the nucleus.  If we were to draw the hydrogen atom above to scale, so that the proton were the size depicted above, the electron would actually be spinning approximately 0.5 km (or about a quarter of a mile) away from the nucleus.  In other words, if the proton was the size depicted above, the whole atom would be about the size of Giants Stadium.  Another peculiarity of this tiny world is the particles themselves.  Protons and neutrons behave like small particles, sort of like tiny billiard balls.  The electron however, has some of the properties of a wave.  In other words, the electron is more similar to a beam of light than it is to a billiard ball.  Thus to represent it as a small particle spinning around a nucleus is slightly misleading.  In actuality, the electron is a wave that surrounds the nucleus of an atom like a cloud.  While this is difficult to imagine, the figure below may help you picture what this might look like:Hydrogen: a proton surrounded by an electron cloud
While you should keep in mind that electrons actually form clouds around their nucleii, we will continue to represent the electron as a spinning particle to keep things simple.
        In an electrically neutral atom, the positively charged protons are always balanced by an equal number of negatively charged electrons.  As we have seen, hydrogen is the simplest atom with only one proton and one electron.  Helium is the 2nd simplest atom.  It has two protons in its nucleus and two electrons spinning around the nucleus.  With helium though, we have to introduce another particle.  Because the 2 protons in the nucleus have the same charge on them, they would tend to repel each other, and the nucleus would fall apart.  To keep the nucleus from pushing apart, helium has two neutrons in its nucleus.  Neutrons have no electrical charge on them and act as a sort of nuclear glue, holding the protons, and thus the nucleus, together.
A Helium Atom
        As you can see, helium is larger than hydrogen.  As you add electrons, protons and neutrons, the size of the atom increases.  We can measure an atom's size in two ways: using the atomic number (Z) or using the atomic mass (A, also known as the mass number).  The atomic number describes the number of protons in an atom.  For hydrogen the atomic number, Z, is equal to 1.  For helium Z = 2.  Since the number of protons equals the number of electrons in the neutral atom, Z also tells you the number of electrons in the atom.  The atomic mass tells you the number of protons plus neutrons in an atom.  Therefore, the atomic mass, A, of hydrogen is 1.  For helium A = 4.Ions and Isotopes
        So far we have only talked about electrically neutral atoms, atoms with no positive or negative charge on them.  Atoms, however, can have electrical charges.  Some atoms can either gain or lose electrons (the number of protons never changes in an atom).  If an atom gains electrons, the atom becomes negatively charged.  If the atom loses electrons, the atom becomes positively charged (because the number of positively charged protons will exceed the number of electrons).  An atom that carries an electrical charge is called an ion.  Listed below are three forms of hydrogen; 2 ions and the electrically neutral form.
 

H+ : a positively charged hydrogen ion	H : the hydrogen atom	H- : a negatively charged hydrogen ion

        Neither the number of protons nor neutrons changes in any of these ions, therefore both the atomic number and the atomic mass remain the same.  While the number of protons for a given atom never changes, the number of neutrons can change.  Two atoms with different numbers of neutrons are called isotopes.  For example, an isotope of hydrogen exists in which the atom contains 1 neutron (commonly called deuterium).  Since the atomic mass is the number of protons plus neutrons, two isotopes of an element will have different atomic masses (however the atomic number, Z, will remain the same).
Two isotopes of hydrogen

Hydrogen Atomic Mass = 1 Atomic Number = 1	Deuterium  Atomic Mass = 2  Atomic Number = 1

Voltage and current in a practical circuit

Because it takes energy to force electrons to flow against the opposition of a resistance, there will be voltage manifested (or "dropped") between any points in a circuit with resistance between them. It is important to note that although the amount of current (the quantity of electrons moving past a given point every second) is uniform in a simple circuit, the amount of voltage (potential energy per unit charge) between different sets of points in a single circuit may vary considerably:

Take this circuit as an example. If we label four points in this circuit with the numbers 1, 2, 3, and 4, we will find that the amount of current conducted through the wire between points 1 and 2 is exactly the same as the amount of current conducted through the lamp (between points 2 and 3). This same quantity of current passes through the wire between points 3 and 4, and through the battery (between points 1 and 4).

However, we will find the voltage appearing between any two of these points to be directly proportional to the resistance within the conductive path between those two points, given that the amount of current along any part of the circuit's path is the same (which, for this simple circuit, it is). In a normal lamp circuit, the resistance of a lamp will be much greater than the resistance of the connecting wires, so we should expect to see a substantial amount of voltage between points 2 and 3, with very little between points 1 and 2, or between 3 and 4. The voltage between points 1 and 4, of course, will be the full amount of "force" offered by the battery, which will be only slightly greater than the voltage across the lamp (between points 2 and 3).

This, again, is analogous to the water reservoir system:

Between points 2 and 3, where the falling water is releasing energy at the water-wheel, there is a difference of pressure between the two points, reflecting the opposition to the flow of water through the water-wheel. From point 1 to point 2, or from point 3 to point 4, where water is flowing freely through reservoirs with little opposition, there is little or no difference of pressure (no potential energy). However, the rate of water flow in this continuous system is the same everywhere (assuming the water levels in both pond and reservoir are unchanging): through the pump, through the water-wheel, and through all the pipes. So it is with simple electric circuits: the rate of electron flow is the same at every point in the circuit, although voltages may differ between different sets of points.

http://www.allaboutcircuits.com/vol_1/chpt_1/6.html

Resistance

One practical and popular use of electric current is for the operation of electric lighting. The simplest form of electric lamp is a tiny metal "filament" inside of a clear glass bulb, which glows white-hot ("incandesces") with heat energy when sufficient electric current passes through it. Like the battery, it has two conductive connection points, one for electrons to enter and the other for electrons to exit.

Connected to a source of voltage, an electric lamp circuit looks something like this:

As the electrons work their way through the thin metal filament of the lamp, they encounter more opposition to motion than they typically would in a thick piece of wire. This opposition to electric current depends on the type of material, its cross-sectional area, and its temperature. It is technically known as resistance. (It can be said that conductors have low resistance and insulators have very high resistance.) This resistance serves to limit the amount of current through the circuit with a given amount of voltage supplied by the battery, as compared with the "short circuit" where we had nothing but a wire joining one end of the voltage source (battery) to the other.

When electrons move against the opposition of resistance, "friction" is generated. Just like mechanical friction, the friction produced by electrons flowing against a resistance manifests itself in the form of heat. The concentrated resistance of a lamp's filament results in a relatively large amount of heat energy dissipated at that filament. This heat energy is enough to cause the filament to glow white-hot, producing light, whereas the wires connecting the lamp to the battery (which have much lower resistance) hardly even get warm while conducting the same amount of current.

As in the case of the short circuit, if the continuity of the circuit is broken at any point, electron flow stops throughout the entire circuit. With a lamp in place, this means that it will stop glowing:

As before, with no flow of electrons, the entire potential (voltage) of the battery is available across the break, waiting for the opportunity of a connection to bridge across that break and permit electron flow again. This condition is known as an open circuit, where a break in the continuity of the circuit prevents current throughout. All it takes is a single break in continuity to "open" a circuit. Once any breaks have been connected once again and the continuity of the circuit re-established, it is known as a closed circuit.

What we see here is the basis for switching lamps on and off by remote switches. Because any break in a circuit's continuity results in current stopping throughout the entire circuit, we can use a device designed to intentionally break that continuity (called a switch), mounted at any convenient location that we can run wires to, to control the flow of electrons in the circuit:

This is how a switch mounted on the wall of a house can control a lamp that is mounted down a long hallway, or even in another room, far away from the switch. The switch itself is constructed of a pair of conductive contacts (usually made of some kind of metal) forced together by a mechanical lever actuator or pushbutton. When the contacts touch each other, electrons are able to flow from one to the other and the circuit's continuity is established; when the contacts are separated, electron flow from one to the other is prevented by the insulation of the air between, and the circuit's continuity is broken.

Perhaps the best kind of switch to show for illustration of the basic principle is the "knife" switch:

A knife switch is nothing more than a conductive lever, free to pivot on a hinge, coming into physical contact with one or more stationary contact points which are also conductive. The switch shown in the above illustration is constructed on a porcelain base (an excellent insulating material), using copper (an excellent conductor) for the "blade" and contact points. The handle is plastic to insulate the operator's hand from the conductive blade of the switch when opening or closing it.

Here is another type of knife switch, with two stationary contacts instead of one:

The particular knife switch shown here has one "blade" but two stationary contacts, meaning that it can make or break more than one circuit. For now this is not terribly important to be aware of, just the basic concept of what a switch is and how it works.

Knife switches are great for illustrating the basic principle of how a switch works, but they present distinct safety problems when used in high-power electric circuits. The exposed conductors in a knife switch make accidental contact with the circuit a distinct possibility, and any sparking that may occur between the moving blade and the stationary contact is free to ignite any nearby flammable materials. Most modern switch designs have their moving conductors and contact points sealed inside an insulating case in order to mitigate these hazards. A photograph of a few modern switch types show how the switching mechanisms are much more concealed than with the knife design:

In keeping with the "open" and "closed" terminology of circuits, a switch that is making contact from one connection terminal to the other (example: a knife switch with the blade fully touching the stationary contact point) provides continuity for electrons to flow through, and is called a closed switch. Conversely, a switch that is breaking continuity (example: a knife switch with the blade not touching the stationary contact point) won't allow electrons to pass through and is called an open switch. This terminology is often confusing to the new student of electronics, because the words "open" and "closed" are commonly understood in the context of a door, where "open" is equated with free passage and "closed" with blockage. With electrical switches, these terms have opposite meaning: "open" means no flow while "closed" means free passage of electrons.

• REVIEW:
• Resistance is the measure of opposition to electric current.
• A short circuit is an electric circuit offering little or no resistance to the flow of electrons. Short circuits are dangerous with high voltage power sources because the high currents encountered can cause large amounts of heat energy to be released.
• An open circuit is one where the continuity has been broken by an interruption in the path for electrons to flow.
• A closed circuit is one that is complete, with good continuity throughout.
• A device designed to open or close a circuit under controlled conditions is called a switch.
• The terms "open" and "closed" refer to switches as well as entire circuits. An open switch is one without continuity: electrons cannot flow through it. A closed switch is one that provides a direct (low resistance) path for electrons to flow through.

refrence : http://www.allaboutcircuits.com/vol_1/chpt_1/5.html