An electromagnetic wave is created by a local disturbance in the electric and magnetic fields magnetic fields. From its origin, the wave can propagate outward in all directions. If the medium in which it is propagating (air for example) is that the same everyplace, the wave can spread out uniformly in all all directions.
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Far from its origin, it will have separated out enough that it
will seem have identical amplitude everywhere on the plane
perpendicular to its direction of travel (in the close to neighbourhood
of the observer). This kind of wave is termed a plane wave. A plane wave
is associate degree idealization that enables one to consider the
complete wave traveling in a very single direction, rather than
spreading move into all directions.
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Electromagnetic waves propagate at the speed of light in a vacuum. In different mediums, like air or glass, the speed of propagation is slower. If the speed of sunshine in a very vacuum is given the image c0, and also the speed in some a medium is c, we will outline the index of refraction, n as:
n = c0 / c
Here is a brief table of the indices of refraction for common media:
substance index of refraction
vaccum 1
air 1.0003
water 1.33
glass 1.55
Reflection
Once a plane wave encounters a change in medium, some or all of it should propagate into the new medium or be reflected from it. The part that enters the new medium is called the transmitted portion and also the different the reflected portion. The part that is reflected incorporates a terribly straightforward rule governing its behaviour. Make the subsequent construction:
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Angle of Incidence = the angle between the direction of
propagation and a line perpendicular to the boundary, on identical face
of the surface. Angle of Reflection = the angle between the direction of
propagation of the reflected wave and a line perpendicular to the
boundary, additionally on identical facet of the surface. Then the rule
for reflection is only expressed as:
The angle of reflection = The angle of incidence
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If the incident medium incorporates a lower index of refraction
then the reflected wave incorporates a 180 degrees part shift upon
reflection. Conversely, if the incident medium incorporates a larger
index of refraction the mirrored wave has no part shift.
Refraction
Once the wave enters the new medium, the speed of propagation will change. In order to match the incident and transmitted wave at the boundary, the transmitted wave can amendment its direction of propagation. As an example, if the new medium has a higher index of refraction, which suggests the speed of propagation is lower, the wavelength can become shorter (frequency should keep identical attributable to the boundary conditions). For the transmitted wave to match the incident wave at the boundary, the direction of propagation of the transmitted wave should be nearer to perpendicular.
The relationship between the angles and indices of refraction is given by Snell's Law:
ni sinqI = nt sinqt
Once the direction of propagation changes, the wave is said to refract. It is most helpful to understand during which direction the wave can refract, not essentially by what proportion.
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The transmitted wave can bend a lot of towards the perpendicular once getting into a medium with higher index of refraction (slower speed of propagation). Example: Why a pool is deeper than it is.
When you explore a pool, the sunshine from very cheap is refracted faraway from the perpendicular, as a result of the index of refraction in air is a smaller amount than in water. To the observer at the side of the pool, the light seems to return from a shallower depth. For identical reason, once you consider objects underwater through a mask, they will appear to be larger than they very area unit. The light from the object is spread outward at the water-air interface of your mask. To you it will seem the object is nearer or larger.
Interference
All magnetism waves may be superimposed upon one another while not limit. The electric and magnetic fields merely add at every purpose. If two waves with the same frequency area unit combined there will a be a relentless interference pattern caused by their superposition. Interference will either be constructive, that means the strength will increase as result, or harmful wherever the strength is reduced. The amount of interference depends of the part distinction at a selected purpose. It may be shown that constructive interference happens for part variations of 0-1200, and 240-3600. so harmful interference happens from 120-2400. for two identical waves, no part shift ends up in total constructive interference, wherever the strength is most and 1800 part shift can produce total harmful interference (no signal at all).
Df = 2pDx/l
Df = 2pDt/T
The phase shift that causes the interference will occur either attributable to a distinction in path length, Dx or a distinction within the time of arrival, Dt the number of part shift, Df
may be computed for these two cases by: Example: Omega may be a radio
navigation system that used the part distinction within the same signal
from 2 fastened transmitters to work out a line-of-position. identical
part distinction corresponded to multiple lines of position separated by
a distance akin to 3600 of part shift. Since the frequency was ten.2
kHz, the wavelength such as 3600 part shift was sixteen miles, that was
the lane dimension on associate degree Omega overprinted chart. Loran-C
additionally incorporates a phase-difference mode with a lane dimension
of solely 3000m since it operates at one hundred kilocycle.
Diffraction
Recall that the perfect plane wave is really infinite in extent. If this wave passes through a gap, known as associate degree aperture, it will split, or opened up, from the gap. The degree to that the cropped wave can opened up depends on the size of the aperture relative to the wavelength. within the extreme case wherever the aperture is extremely massive compared to the wavelength, the wave can see no impact and will not split in the least. At the opposite extreme, if the gap is extremely tiny, the wave can behave as if it were at its origin and opened up uniformly all told directions from the aperture. In between, there will be a point of optical phenomenon.
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First take into account a circular aperture. If a wave with
wavelength l encounters a gap with diameter D, the number of optical
phenomenon as measured by the angle, q ,at that the new wave diverges from the gap, measured from edge to edge, are going to be approximated by
q = l/D
Comments on this formula:
- The symbol is employed to point associate degree approximate result, as against an explicit relationship. This result is solely valid for comparatively tiny angles, one thing but concerning 20 degrees.
- There is some ambiguity in what is meant by this angle. Essentially, the wave does not merely finish at this boundary, however falls off swimmingly. The precise purpose that defines the extent of the wave may be a matter of definition and there area unit 2 customary conventions: the one employed in this book is that the ½ power or -3 decibel definition.
- The issue of 2 is additionally associate degree approximation. A a lot of correct description needs elaborate information concerning the form of the aperture
- The angle q should be in radians!
By RR Team
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Pattabhi Foundation
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