Explanation
S1 : When light reflects from denser med. (Glass) a phase shift of π it is generated.
S2 : Centre maxima or minima depends on thickness of the lens.
Obviously (2) is denser because ray bends towards normal.
When a light wave travel from a rarer to a denser medium it loses speed, but energy carried by the wave does not depend on its speed. Instead, it depends on the amplitude of wave.
A narrow pulse is made of harmonic waves with a large range of wavelength. As speed of propagation is different for different wavelength, the pulse cannot retain its shape while travelling through the medium.
The central spot of Newton’s rings is dark when the medium between piano convex lens and plane glass is rarer than the medium of lens and glass. The central spot is dark because the phase change of π it is introduced between the rays reflected from surfaces of denser to rarer and rarer to denser medium.
When one of slits is covered with cellophane paper, the intensity of light emerging from the slit is decreased (because this medium is translucent). Now the two interfering beam have different intensities or amplitudes. Hence intensity at minima will not be zero and fringes will become indistinct.
When a polaroid is rotated in the path of unpolarised light, the intensity of light transmitted from polaroid remains undiminished (because unpolarised light contains waves vibrating in all possible planes with equal probability). However, when the polaroid is rotated in path of plane polarised light, its intensity will vary from maximum (when the vibrations of the plane polarised light arc parallel to the axis of the polaroid) to minimum (when the direction of the vibrations becomes perpendicular to the axis of the crystal). Thus using polaroid we can easily verify that whether the light is polarised or not.
Doppler’s effect is observed readily in sound wave due to larger wavelengths. The same is not the case with light due to shorter wavelength in every day life.
In Young’s experiments fringe width for dark and white fringes are same while in Young’s double slit experiment when a white light as a source is used, the central fringe is white around which few coloured fringes are observed on either side.
It is quite clear that the coloured spectrum is seen due to diffraction of white light on passing through fine slits made by fine threads in the muslin cloth.
As the wave diffracted from the edges of circular obstacle, placed in the path of light interfere constructively at the centre of the shadow resulting in the formation of a bright spot.
The beautiful colours are seen on account of interfrerence of light reflected from the upper and the lower surfaces of the thin films.
Microwave communication is preferred over optical communication because microwaves provide large number of channels and wider band width compared to optical signals as information carrying capacity is directly proportional to hand width. So, wide the band width, greater the information carrying capacity.
The clouds consists of dust particles and water droplets. Their size is very large as compared to the wavelength of the incident light from the sun. So there is very little scattering of light. Hence the light which we receive through the clouds has all the colours of light. As a result of this, we receive almost white light. Therefore, the cloud are generally white.
In sky wave propagation, the radio waves having frequency range 2 MHz to 30 MHz are reflected back by the ionosphere. Radio waves having frequency nearly greater than 30 MHz penetrates the ionosphere and is not reflected back by the ionosphere . The TV signal having frequency greater than 30 MHz therefore cannot be propagated through sky wave propagation. In case of sky wave propagation, critical frequency is defined as the highest frequency is returned to the each by the considered layer of the ionosphere after having sent straight to it. Above this frequency, a wave will penetrate the ionosphere and is not reflected by it.
The television signals being of high frequency are not reflected by the ionosphere. So the TV signals are broadcasted by tall antenna to get large coverage, hut for transmission over large distance satellites are needed. That is way. satellites are used for long distance iv transmission.
We know, with increase in altitude, the atmospheric pressure decreases. The high energy particles (i.e., γ-rays and cosmic rays) coming from outer space and entering out earth’s atmosphere cause ionisation of the atoms of the gases present there. The ionising power of these radiation decreases rapidly as they approach to earth, due to increase in number of collisions with the gas atoms. It is due to this reason the electrical conductivity of earth’s atmosphere increase with altitude.
Hertz experimentally observed that the production of spark between the detector gap is maximum when it is placed parallel to source gap. This means that the electric vector of radiation produced by the source gap is parallel to the two gaps i.e., in the direction perpendicular to the direction of propagation of the radiation.
The earth’s atmosphere is transparent to visible light and radio waves, but absorbs X-axis. Therefore X-rays telescope cannot be used on earth surface.
Short wave (wavelength 30 km to 30 cm). These waves are used for radio transmission and for general communication purpose to a longer distance from
ionosphere.
The wavelength of these waves ranges between 4000 Å to 100 Å that is smaller wavelength and higher frequency. They are absorbed by atmosphere and convert oxygen into ozone. They cause skin diseases and they arc harmful to eye and cause permanent blindness.
Ozone layer in the stratosphere helps in protecting life of organism from ultraviolet radiation on earth. Ozone layer is depleted due to of several factors like use of chlorofluoro carbon (CFC) which is the cause of environmental damages.
Radio waves can be polarised because they are transverse in nature. Sound waves in air are longitudinal in nature.
In the absence of atmosphere, all the heat will escape from earth’s surface which will make earth in hospitably cold.
Light radiations and thermal radiations both belong to electromagnetic spectrum. Light radiation belongs to visible while thermal radiation belongs to infrared region of EM spectrum.
Also EM radiations required no medium for propagation.
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