Light is form of energy that enables us to see and makes plants grow. A light beam can travel through empty space.So this energy does not use the air or other material through which it passes in order to travel.The energy must must therefore be carried by the beam itself.
We can tell from the sharp edges of shadows that rays of light travel through air along straight path.They cannot bend round corners.
Animation showing different Wave Form of Light
People therefore thought of light rays as straight lines. They help to explain reflection and refraction. Then in 1680,Huygens suggested that light rays were in fact waves. Over a century later his theory was shown to be true.
Light travels in one direction but the ray itself is moving up and down in continuous crests and troughs.This wave has a similar shape to ripples on a pond.As it moves through space,there is always the same distance between two neighbouring crests or troughs. The distance is called the wavelength.It is an extremely tiny distance measured in minute fractions of a meter.The height of a crest or the depth of a trough is called the amplitude.The greater the amplitude of the wave, the greater its energy.As the energy decreases, the amplitude grows less and less.
|Graphical Representation Wavelength and Direction of Light Wave|
After the wave has gone through one crest and one trough it has travelled one wavelength.The wave has completed one cycle of its motion and is read to repeat itself.The number of cycles in one second is called the frequency of the wave.
Waves move at tremendous speed.The speed is always the same in one particular medium such as air,but decreases when waves enter denser material,such as glass or water.This change in speed causes refraction of the light beam producing an increase in wavelength.The speed of a light wave in any medium equals its wavelength multiplied by its frequency . The greatest speed of light is in a vacuum,such as outer space .The speed in air is very close to this value.The maximum speed is equal to 300,000 Km per second .No object moving in a vacuum can travel faster than this speed.
Each light wave has its own wavelength and each of these wavelengths corresponds to a slightly different color.Red light has almost twice the wavelength of violet light .Yellow.green and blue light have wavelengths between these values.
Light is not the only form of energy transmitted in waves , Radio waves, infrared and ultraviolet radiation,X-ray and gamma rays also travel as wave motions.All these waves move at the speed of light .However,the wave lengths (and hence frequencies) are very different. It is the different wavelengths that give each type of radiation its special properties.They are all examples of electromagnetic radiation, and they all travel as electromagnetic waves.
The chart showing the different electromagnetic radiations in order of increasing wavelength (or decreasing frequency) is called the electromagnetic spectrum.
|Graphical Representation of Different wave length of Visible colored light|
Wave lengths of Red light is almost twice that of blue light .The frequency is that the number of complete wave cycle in one second. As the wavelength increases the frequency decreases .Red light has almost twice the wavelength of blue light while its frequency is almost half that of blue light.
|Graphical relation of light wave energy and amplitude|
The amplitude or maximum height of a crest or trough,remains the same if the wave`s energy stays the same .If the wave loses the energy , the amplitude decreases. The square of the amplitude (amplitude times amplitude)gives a measure of the energy.
The electromagnetic spectrum. Radio waves have much longer wavelengths than light waves which in turn have greater wavelengths than X-rays and gamma rays .We can only see a very narrow part of the spectrum.
|Wilhelm Conrad Röntgen : was a German physicist, who, on 8 November 1895, produced and detected electromagnetic radiation in a wavelength range today known as X-rays|
Like light, X-rays also move as waves, but the wavelength is very much smaller. Unlike light waves, they are invisible.The energy of X-rays is very high. They can travel a great distance inside an object and sometimes they are able to pass straight through it.
X-rays are produced in an X-ray tube when a narrow stream of electrons emitted from a heated cathode is strongly attracted towards the anode.The anode is at a very high voltage.This means that the electrons move very fast towards the anode and therefore have a large amount of energy.The anode contains a small disc of heavy metal such as Tungsten.When the electrons strike the tungsten atoms, They give up their energy to electrons in the atoms.To get rid of this excess energy , the atoms emit X-rays.
|Full Picture of X-Ray Machine|
X-rays have various uses in medicine X-rays, like light, acn produce an image on photographic film .If a person stand between a low energy source of X-rays and a film , a photo of the bone structure is obtained .Broken or badly formed bones can be seen.
A more advanced type of X-ray machine is the computerized tomographic (CT) scanner. A CT scanner uses a computer to be produce highly detailed pictures of the inside of a patient`s body. The computer in a CT machine is fed data on how the different tissues in the body absorb X-rays.As a patient is scanned , the computer compares this data with the amount of radiation actually absorbed by the patient`s body.The computer is able to build up a very detailed picture of the tissues in the body.
To Produce a CT scan ,X-rays are only passed through a thin slice of the body at one time .This also helps produce a clearer picture .The X-ray tube travels around the patient`s body , making 1.5 million exposures as it travels. Sensitive detectors also travel around the body opposite the X-ray tube.The detectors are linked to the computer which builds up the detailed picture on a television -like screen.Today`s scanners can examine slices of the body from 2 mm to 13 mm thick,as easily as if they were slices of bread.
Another type of body scanner is called an NMR scanner.This uses a process called nuclear magnetic resonance (NMR) to produce detailed pictures of the inside of a patient`s body.The patient lies in a strong magnetic field produced by an electric current flowing in a superconducting coil.Radio signals are beamed into the area of the body being investigated .The nuclei or central parts, of the atoms of the body produced magnetic signals which are picked up by detectors. A computer is used to form a picture of the inside of the body from the magnetic signals.
|Picture of MRI Scanner|
X-rays are also used in scientific research to find out how atoms and molecules are arranged in crystals and how they are grouped together in some of then giant chemical compounds found in the body,such as DNA.This type of research is called x-ray crystallography.
|3D Picture of Diode as Rectifier|
The diode . An alternating voltage makes the anode positive and then negative in one cycle as current will only flow when the anode is positive , the negative half of the cycle is lost .Alternating current is thus changed to direct current .The diode therefore acts as a rectifier.
3-D diagram of an x-ray tube. The cathode is specially shaped so that a narrow beam of electrons is directed onto the tungsten disc in the anode .This produces a fairly narrow beam of X-rays which leaves the tube through a thin metal plate .The energy of the X-rays depends on the difference in voltage between anode and cathode.
Röntgen : was a German physicist, who, on 8 November 1895, produced and
detected electromagnetic radiation in a wavelength range today known as
An X-ray photograph of a hand with a ring .Dentists take X-ray photos to check that your teeth are growing correctly and to see if you need any fillings. Only bones and show up on the negative of the film. The film is blackened by X-rays which are able to pass straight through the skin and air . Bones and teeth absorb most of the X-rays and therefore appear whitish on the negative and dark on the print.
The chemical structure of cytochrome C. This is the giant molecule present in the cells of the body .Its complicated structure was unravelled by the use of X-rays. Each colored ball represent a different group of atoms .Knowing its structure helps scientist to learn about how it works.
|Computer Generated 3D Model of Cytochrome C Through X-Ray Crystallography Technique|
|X-Ray Crystallography Technique require to create a 3d Model in computer of any complex protein structure|