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viney kumar sharma Grade: 12
        explain polarisation.light is transverse.polarisation means either electric component or magnetic component is absent.how can be light with only 1 field as 1 field generates other??
8 years ago

Answers : (3)

AskIITians Expert Hari Shankar IITD
17 Points
										

Hi,


 


Your concept of polarization is incorrect. Polarization DOES NOT MEAN that electric/ magnetic field is absent.


Light is an Electromagnetic wave. All EM waves are transverse. This means that the oscillaitions of electric and magnetic fields takes place in a plane perpendicular to the direction of propogation. Now, there are an infinite number of directions perpendicular to the diretion of propogation. Electric field can oscillate in any of these directions. This is what happens in unpolarized light. Electric field oscillates in all possible directions perpendicular to the direction of light.



In the figure, the red plane is the plane perpendicular to the direction of propogation. So, the electic field can oscillate in any of the green lines. There are infinitely many green lines, so there can be infinitely many directions of electric field variation. On the other hand, in POLARIZED light, the electric field varying along only one green line is present. All other directions of electric field variation(green lines) are filtered out.


The magnetic field is still present. But since the electric field is varying only in one direction, magnetic field also varies only in one direction in polarized light. Check out wikipedia for more information on polarization and do tell me if you didn't get it.


 


 


 

8 years ago
AskIITianExpert Srijan.iitd
8 Points
										

Light can be represented as a transverse electromagnetic wave made up of mutually perpendicular, fluctuating electric and magnetic fields. The left side of the following diagram shows the electric field in the xy plane, the magnetic field in the xz plane and the propagation of the wave in the x direction. The right half shows a line tracing out the electric field vector as it propagates. Traditionally, only the electric field vector is dealt with because the magnetic field component is essentially the same.



This sinusoidally varying electric field can be thought of as a length of rope held by two children at opposite ends. The children begin to displace the ends in such a way that the rope moves in a plane, either up and down, left and right, or at any angle in between.


Ordinary white light is made up of waves that fluctuate at all possible angles. Light is considered to be "linearly polarized" when it contains waves that only fluctuate in one specific plane. It is as if the rope is strung through a picket fence -- the wave can move up and down, but motion is blocked in any other direction. A polarizer is a material that allows only light with a specific angle of vibration to pass through. The direction of fluctuation passed by the polarizer is called the "easy" axis.


If two polarizers are set up in series so that their optical axes are parallel, light passes through both. However, if the axes are set up 90 degrees apart (crossed), the polarized light from the first is extinguished by the second. As the angle rotates from 0 to 90 degrees, the amount of light that is transmitted decreases.


 


for your doubt i shud say that polarization dont eliminates one field but just elimintes light waves whose fields are not alingned to the angle of polarizer.I think its clear now!!!

8 years ago
Vishal Vaibhav
6 Points
										"Your concept of polarization is incorrect. Polarization DOES NOT MEAN that electric/ magnetic field is absent.


Light is an Electromagnetic wave. All EM waves are transverse......"

Just a correction: NOT all EM waves are transverse. ONLY plane EM waves are transverse .i.e.
E(r,t)=Re{E_0*exp[i*(x*k_x+y*k_y+z*k_z+omega*t)]}
where r=(x,y,z) is the position vector and k=(k_x,k_y,k_z) in the wave vector.

Nature of the EM waves has to be determined from the possible solutions of the Maxwell's equations along with the boundary conditions. A simple example is a dielectric wave guide where it is possible to have HYBRID MODES which neither transverse form Magnetic field nor for the Electric field.

8 years ago
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