Speed of light
Wave optics is the branch of opticswhich deals with interference, diffraction, polarization, and other phenomena of light.
Electromagnetic spectrum
Electromagnetic spectrum is the distribution of electromagnetic radiation of all possible frequencies and wavelengths.
Electromagnetic spectrum is classified are as follows:
Radio waves: Frequency of these waves ranges from few Hz to 109 Hz. Radio waves emitted by radio stations. Radio waves are also emitted by stars and gases in space.
Microwaves: Frequency of these waves ranges from109 Hz to 3.0 *1011Hz.The wavelength of microwaves is greater than 1mm and less than 30cm.It is used byastronomers to learn about the structure of nearby galaxies.
Infrared: Frequency of these waves ranges from 3.0 *1011Hz to 109 Hz. The wavelength of infrared is 1nm to 700nm. In space; infrared light helps us map thedust between stars.
Visible: Frequency of these waves ranges from 4.3 *1014 Hz to7.5 * 1014 Hz.The wavelength of visible light is 400nm to 700nm.Our eyes detect visible light. Fireflies, light bulbs, and stars all emit visible light.
Ultraviolet: Frequency of these waves ranges from 7.5 * 1014 Hz to 5.0 *1015 Hz .The wavelength of ultraviolet rays is 400nm to 60nm Ultraviolet radiation is emitted by the Sun and are the reason skin tans and burns. "Hot" objects in space emit UV radiation as well.
X-ray: Frequency of these waves ranges from 5.0 *1015Hz to3.0* 1018 Hz.The wavelength of X-ray is 60nm to 10-8nm. Hot gases in the Universe also emit X-rays.
Gamma ray: Frequency of these waves rangesfrom 3.0*1018 Hz to3.0 * 1022 Hz. The wavelength of Gamma rays is 0.1nm to 10-5nm. Doctors use gamma-ray imaging to see inside body. The biggest gamma-ray generator of all is the Universe.
Wavelets
Wavelets are the disturbance of the point source but the point source is taken in the primary wave front. Wavelets formed by the locus of the virtual source.
Wave lets are of two types:
a. Primary wavelets and
b. Secondary wavelets.
Wave front
During the propagation of the wave, all the particles of the medium which are located at the same distance from the source receive the disturbance simultaneously and vibrate in the same phase. Thus, a wave front of light at any instance is the locus of all particles of the medium vibrating in the same phase at that time. The shape of wave front depends on the nature of source and the disturbance of the wave front from the source. That is wave front. Wave front is the disturbance of the point source. Wave front formed by the locus of the real source. Wave fronts are of three types:
a. Spherical wave front
b. Cylindrical wave front
c. Plane wave front.
Huygens principle
Huygens’s principle states that:
a. Each point on the primary wave front acts as a source of secondary wave lets, sending out disturbance in all direction in a similar manner as the original source of the light does.
b. The new position of the wave front at any instant is given by the forward envelope of the secondary wavelets at that instant.
Consider a point source of light. Let XY be the section of the spherical wave front at any time t. supposed we are interested in finding the new position of the wave front at time t+∆t. to do so, a number of points a,b,c,d are the point taken on the primary wave front. These point acts as the source of secondary wavelets. In time ∆t light will travel a distance c∆t. taking the point a,b,c,d,…as the centre of sphere each of radius c∆t are drawn. The forward enveloped X’Y’ of these spheres give the position of wave front at ∆t +t and called secondary wave front.
Laws of reflection on the basis of wave theory
The advantages of Michelson’s method are:
The distance between the two stations is very large.
Images obtained are very bright so that position can be determined accurately.
There is no measurement of the displacement of image.
The disadvantages are:
It is very difficult to maintain the high speed rotation of mirror.
High speed of the rotation of the mirror can break the mirror.
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