How light bulb glows?

An LED lamp uses light emitting diode as the source which comes under solid state devices.It offers long life and energy efficiency with low cost than those of fluorescent and incandescent lamps.

The chassis of the bulb is made of ceramic and houses the electronic ballast. Ceramic is used for its insulating and heat dissipative properties. The LED bulb is housed inside a phosphor coated glass dome.Remote phosphor is used to provide constant wavelength and enhance light output.  This also enables the LED to emit only a single colored light throughout its lifetime while also reducing glare at the same time.

Courtesy:engineersgarage.com

Hardwork Can Never Ever Fails...

Best Luck...

Tubelight starter-working

Nowadays, fluorescent lights are mostly used lighting system.It is being filled with mercury vapor.Electric charges are used to excite mercury atoms to provide ultraviolet light.starter is used in the tube light circuit to provide an initial current to filaments of the tube light.Look below to understand the purpose of starter.

Current will not pass in to the circuit as soon as the switch is pressed because the gas inside it is not ionized and the tube light behaves a open circuit.  Once the gas is ionized, it will provide a conduction path for the current to flow.Hence to ionize,an initial high is required for a short period of time across the filament of the main tube.This work is being done by a starter.
By conclusion,
To make the tube light to be ON ,it must be ionized using the starter current.

Courtesy:engineersgarage.com

Hardwork Can Never Ever Fails..
Best Luck...

CLAMP METER

Clamp meters are a very convenient testing instrument that permits current measurements on a live conductor without circuit interruption. When making current measurements with the ordinary multimeter, we need to cut wiring and connect the instrument to the circuit under test as shown in Fig.1.
Using the clamp meter, however, we can measure current by simply clamping on a conductor as illustrated in Fig.2. One of the advantages of this method is that we can even measure a large current without shutting off the circuit being tested.

Fig 1: Measurment using multimeter

Fig 2:Measument using clamp meter

HOW DOES A DC CLAMP METER WORKS:

Ordinary clampmeters used to measure AC currents work on the principle of electromagnetic induction caused by the alternating current flowing in the conductor which reverses direction causing a dynamically changing magnetic field. However, in DC conductors, the current flows in a fixed polarity. Consequently, the magnetic field around the conductor is fixed and does not change. Hence, a conventional clamp meter will register no reading.

A DC clamp meter works on the principle of the Hall Effect. The Hall Effect, named after Edwin Hall who discovered it 1879, states that when a conductor carrying current is placed in a magnetic field, a potential is induced across the conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current. It is caused as the charge carriers, electrons or holes, experience a force known as the Lorentz force and are pushed to the sides of the conductor.

In general AC clamp meters operate on the principle of current transformer(CT) used to pick up magnetic flux generated as a result of current flowing through a conductor. Assuming a current flowing through a conductor to be the primary current, you can obtain a current proportional to the primary current by electromagnetic induction from the secondary side(winding) of the transformer which is connected to a measuring circuit of the instrument. This permits you to take an AC current reading on the digital display(in the case of digital clamp meters) as illustrated by the block diagram.

A clampmeter which works on the Hall effect has a sensor known as the Hall element. The Hall element is subjected to the magnetic field caused by the flow of current to be measured. This causes a small voltage across the Hall element. This voltage is amplified and measured.

coutesy       : www.electrotechnik.net
                       www.kew-ltd.co

Cellular Repeater

A cellular repeater may be considered as a form of bi-directional amplifier. They will receive a signal from the local base-station and then re-broadcast it locally within the users premises - house, office, etc. The signal transmitted by the cellular handset or user equipment is packed up by the repeater and rebroadcast to the base-station.

Typically a cellular repeater will utilise an external directional antenna to communicate with the base station. There will then be a down lead to the repeater unit itself which will contain the antenna for radiating the signal within the premises.

Many simple cellular repeaters only allow use by one cell phone, but others allow the use of multiple phones.

In order to reduce cellular interference and congestion, the cellular repeater will transmit and receive on the same frequency. 

Repeater

Radio Communication

Sound and radio waves are different phenomena. Sound consists of pressure variations in matter, such as air or water. Sound will not travel through a vacuum. Radio waves, like visible light, infrared, ultraviolet, X-rays and gamma rays, are electromagnetic waves that do travel through a vacuum. When you turn on a radio you hear sounds because the transmitter at the radio station has converted the sound waves into electromagnetic waves, which are then encoded onto an electromagnetic wave in the radio frequency range (generally in the range of 500-1600 kHz for AM stations, or 86-107 MHz for FM stations). Radio electromagnetic waves are used because they can travel very large distances through the atmosphere without being greatly attenuated due to scattering or absorption. Your radio receives the radio waves, decodes this information, and uses a speaker to change it back into a sound wave. An animated illustration of this process is given below (mouse-over the images for animations).

• A sound wave is produced with a frequency of 5 Hz - 20 kHz.                                                                                                    
• The sound wave is equivalent to a pressure wave traveling through the air.

• A microphone converts the sound wave into an electrical signal.

•    The electrical wave traveling through the microphone wire is analogous to the original sound wave. 
• The electrical wave is used to encode or modulate a high-frequency "carrier" radio wave. The carrier wave itself does not include any of the sound information until it has been modulated.
• The carrier wave can either be amplitude modulated by the electrical signal, or frequency modulated.
• 
• The signal is transmitted by a radio broadcast tower.
• 
• Your radio contains an antennato detect the transmitted signal, a tuner to pick out the desired frequency, a demodulator to extract the original sound wave from the transmitted signal, and an amplifier which sends the signal to the speakers. The speakers convert the electrical signal into physical vibrations (sound).

Clock Skew and jitter in digital

Jitter is nothing but the displacement of signal from its original position.This movement may lag or lead from its original or ideal position.As a speed increases, the edge deviation cause a significant problems like signal integrity,skew,race condition and other timing problems.

Classification 

1. cycle-to-cycle jitter

Cycle-to-cycle jitter is the change in an output’s transition in time in relation to the transition during the previous cycle.

2.period jitter

Period jitter is the maximum change in a signal transition from the ideal position in time. Phase jitter, also called long-term jitter, in the maximum change in an output signal transition from its ideal position over many cycles (typically 10 to 20 microseconds).

3.phase jitter

Phase jitter may leads to the displacement of phase from one signal to another.

Figure A: cycle to cycle jitter

 skew

Skew deals with the propagation delay of the output signal.It is the variation of propagation delay differences between output signals.Excessive skew, especially for clock signals, can cause race conditions and other timing errors that result in system data faults. At the very least, poor skew will force a slower maximum system speed, and this, in turn, will limit system performance.

 

 Hardwork Can Never Ever Fails...

 Best Luck....

Sound Waves

SOUND:

Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing.Sound also travels through plasma.

Sound is a sequence of waves of pressure that propagates through compressible media such as air or water. Sound that is perceptible by humans has frequencies from about 20 Hz to 20,000 Hz.

The behavior of sound propagation is generally affected by three things:

• A relationship between density and pressure. This relationship, affected by temperature, determines the speed of sound within 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.
• The viscosity of the medium also affects the motion of sound waves. It determines the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible.

simple simulation of sound waves traveling in air

Longitudinal Waves and Tuning Forks

Sound waves are produced by vibrating objects. Whether it be the sound of a person's voice, the sound of a piano, the sound of a trombone or the sound of a physics book slamming to the floor, the source of the sound is always a vibrating object.

A tuning fork serves as a useful illustration of how a vibrating object can produce sound. The fork consists of a handle and two tines. When the tuning fork is hit with a rubber hammer, the tines begin to vibrate. The back and forth vibration of the tines produce disturbances of surrounding air molecules. As a tine stretches outward from its usual position, it compresses surrounding air molecules into a small region of space, this creates a high pressure region next to the tine.

As the tine then moves inward from its usual position, air surrounding the tine expands; this produces a low pressure region next to the tine. The high pressure regions are known as compressions and the low pressure regions are known as rarefactions. As the tines continue to vibrate, an alternating pattern of high and low pressure regions are created. These regions are transported through the surrounding air, carrying the sound signal from one location to another.




Sound waves of Tuning Fork

Here is the link shows the animation on the sound waves.....

Animations of Sound Waves

Energy levels and radiations-Animation

Electrons in a hydrogen atom must be in one of the allowed energy levels. If an electron is in the first energy level, it must have exactly -13.6 eV of energy. If it is in the second energy level, it must have -3.4 eV of energy. An electron in a hydrogen atom cannot have -9 eV, -8 eV or any other value in between.

Let's say the electron wants to jump from the first energy level, n = 1, to the second energy level n = 2. The second energy level has higher energy than the first, so to move from n = 1 to n = 2, the electron needs to gain energy. It needs to gain (-3.4) - (-13.6) = 10.2 eV of energy to make it up to the second energy level.

The electron can gain the energy it needs by absorbing light. If the electron jumps from the second energy level down to the first energy level, it must give off some energy by emitting light. The atom absorbs or emits light in discrete packets called photons, and each photon has a definite energy. Only a photon with an energy of exactly 10.2 eV can be absorbed or emitted when the electron jumps between the n = 1 and n = 2 energy levels.
The energy that a photon carries depends on its wavelength. Since the photons absorbed or emitted by electrons jumping between the n = 1 and n = 2 energy levels must have exactly 10.2 eV of energy, the light absorbed or emitted must have a definite wavelength. This wavelength can be found from the equation
E = hc/l,
where E is the energy of the photon (in eV), h is Planck's constant (4.14 x 10^-15 eV s) and c is the speed of light (3 x 10⁸ m/s). Rearranging this equation to find the wavelength gives
l = hc/E.
A photon with an energy of 10.2 eV has a wavelength of 1.21 x 10^-7 m, in the ultraviolet part of the spectrum. So when an electron wants to jump from n = 1 to n = 2, it must absorb a photon of ultraviolet light. When an electron drops from n = 2 to n = 1, it emits a photon of ultraviolet light.
The step from the second energy level to the third is much smaller. It takes only 1.89 eV of energy for this jump. It takes even less energy to jump from the third energy level to the fourth, and even less from the fourth to the fifth.
What would happen if the electron gained enough energy to make it all the way to 0eV? The electron would then be free of the hydrogen atom. The atom would be missing an electron, and would become a hydrogen ion.




Click below to view the animation
Energy level animation


Hardwork Can Never Ever Fails.
Best luck..

Introduction to electrons in crystals

A meaningful discussion of semi­conductors requires some background on how electrons move through solids. The free-electron gas model simply assumes that the electrons move through an empty periodic box. But of course, to describe a real solid the box should really be filled with the countless atoms around which the conduction electrons move. 

Click below to view the animation
electrons animation



Hardwork Can Never Ever Fails..
Best Luck..

ULTRA SOUND

Ultra Sound:
Ultrasound is a cyclic sound pressure wave with a frequency greater than the upper limit of the human hearing range. Ultrasound is thus not separated from audible sound based on differences in physical properties only the fact that humans cannot hear it.
Ultrasound is used in many different fields. Ultrasonic devices are used to detect objects and measure distances. Ultrasonic imaging is used in human and veterinary medicine. In non-destructive testing of products and structures, ultrasound is used to detect invisible flaws. For Industries, ultrasound is used for cleaning and for mixing, and to accelerate chemical processes. 

Ultrasonics is the application of ultrasound. Ultrasound can be used for imaging, detection, measurement, and cleaning. At higher power levels ultrasonics are useful for changing the chemical properties of substances.



Figure. Ranges of Ultra sound

A common use of ultrasound is in range finding; this use is also called SONAR, (sound navigation and ranging). An ultrasonic pulse is generated in a particular direction. If there is an object in the path of this pulse, part or all of the pulse will be reflected back to the transmitter as an echo and can be detected through the receiver path. By measuring the difference in time between the pulse being transmitted and the echo being received, it is possible to determine the distance.


Principle of Active SONAR

Here is the animation for the Ultrasound....

Animation of ultra sound

Distributed Antenna System (DAS)

The concept of a Distributed Antenna System, DAS has many advantages in some applications. A Distributed antenna system, DAS is a network of antennas spaced apart from each other, but connected to a common source. In this way the DAS is able to provide wireless or radio coverage within a given area.

The idea of a distributed antenna system is being adopted increasingly as it enables a number of advantages to be gained. However this is at the cost of a larger more complicated system. Nevertheless, distributed antenna systems are being used in a variety of areas to enable the right coverage to be gained for several applications.

Although the concept of distributed antenna systems has been known about for many years, it is with the increased deployment of wireless systems within buildings and other difficult coverage areas that the idea of distributed antenna systems has come to the fore.

Advantages of using a distributed antenna system

• Better defined coverage
• Fewer coverage holes
• Same coverage using a lower overall power
• Lowers health risk as a result of using lower overall power levels
• Individual antennas do not need to be as high as a single antenna for the equivalent coverage

Disadvantages of using a distributed antenna system

• Higher cost as a result of additional infrastructure required
• Possible greater visual impact in some applications as a result of greater number of antennas, although they are likely to be much lower in height.

Basic concept of a distributed antenna system

The basic idea behind the distributed antenna system is to utilise several different antennas over the required coverage area. Using this approach the overall power required is less because these more localised antennas can be placed more effectively for a small area, rather than having a single, larger antenna that is a compromise for the wider coverage needed. By adopting a distributed antenna system approach, this helps overcome the shadowing and penetration losses because a line of sight link is available more frequently. As a result the levels of absorption are lower and this means the overall power levels can be reduced.

www.RadioElectronics.com