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Wednesday, 25 February 2015

Nature Of Light

theory of light


Light and related phenomena have always had a great fascination for humans. Just the daily observation of day and night - light and dark - and the twinkling of stars suggests, the fascination this must have had on early humans. The optical color outdoor games such as Halo, Rainbow and Northern Lights, win a majority of their enchantment by the luminosity of the associated phenomena. So it is not surprising that mankind busy early with light and the history of light is closely linked with the history of physics.

Probably the earliest tradition of applications of optics exists from antiquity. First scientific papers come from the Arab world of the Middle Ages. In the 13th century that Roger Bacon to find systematic studies of refractive lens maker equation. Based on this, the first glasses were developed in the 15th century. In accordance with the principles of geometrical optics were known in the 17th century. Reflection and refraction were understood and most atmospheric optical phenomena, such as the emergence of the rainbow could be explained.

The question of the nature of light was detected only in the 18th century and also the same central element of a fierce debate. On the one hand there were the schools to the Dutchman Christian Huygens and the Englishman Robert Hooke. Both interpretations of light as a wave, similar to how it was used, for example, of water waves. The other school was led by Isaac Newton. In keeping with its Newton's laws and their mechanical interpretation of the world as he understood light particle, which divided by their different pulse in the different colors.

These views were manifested by the postulation of Maxwell's equations in which James C. Maxwell had 1864 combined electric and magnetic phenomena in four equations. Through the clever manipulation he had encountered two wave equations, so that the existence of waves seemed possible, which were characterized by an oscillation of electric and magnetic fields. A short time later, Heinrich Hertz actually managed the experimental proof of this electro-magnetic waves. Thus, it became clear that light was a special form of this new wave. The electromagnetic spectrum spans an enormous frequency or wavelength range. The visible light is only a very small proportion of this total area. It also includes radio waves, microwaves, infrared, ultraviolet, X-rays and gamma rays it.

Synchronous Motor

Motor

Synchronous motors are a type of alternating current motor in which the rotation of the shaft is synchronized with the frequency of the feed stream; the rotation period is exactly equal to an integer number of cycles CA. Its rotation speed is constant and depends on the frequency of the mains voltage to which it is connected and the number of pole pairs of the motor, this speed being known as "synchronous speed". This type of engine has electromagnets in the stator of the motor create a

Rotating magnetic field in time synchronicity at this speed.

The mathematical expression that relates the speed of the machine with the above parameters is:

n = \ frac {60 \ cdot f} {P} = \ frac {120 \ cdot f} {p}
where:

f: frequency of the network that is connected machine (Hz)
P: Number of pole pairs having the machine
p: Number of poles having the machine
n: Synchronous speed of the machine (RPM)

For example, if a machine has four poles (two pole pairs) connected to a 50 Hz grid, the machine will operate at 1500 rpm.

They work much like an alternator. Within the family of synchronous motors must distinguish:

Synchronous motors.

Asynchronous motors synchronized.
The permanent magnet motors.
Synchronous motors are called so because the rotor speed and the speed of the stator magnetic field are equal. Synchronous motors are used in large machines with a variable load and need a constant speed.

Braking phase synchronous motor 

Generally, the desired speed of this engine is adjusted by a rheostat. The synchronous motor, when it reaches the critical torque stop, not being the most orthodox way to do it. The critical torque is reached when the engine load exceeds the allocated torque. This causes overheating which can damage the engine. The best way is to vary the load until the current consumption of the network as low as possible, and then disconnect the motor.

Another way, and most common, is regulating rheostat thereby vary the intensity and can disconnect the motor safely.