a long time, the founders of wave optics T. Young and A. Fresnel knew that the light waves are longitudinal, ie, they are similar to sound waves.While light waves are perceived as elastic waves in the air that fills the entire space and penetrate into each body.It seemed that such waves can not be called transverse.
Yet gradually gaining more experimental evidence and facts that could not be explained by assuming that the light waves - longitudinal.After transverse waves can only exist in solids.But how can the body move in a solid live without resistance?Ether also does not have to slow down the movement of bodies.Otherwise the law of inertia would not be satisfied.
can be considered a simple and useful experiment with a crystal of tourmaline.It is transparent and has a green color.
have tourmaline crystal has a symmetry axis.This crystal is referred to the uniaxial crystal.Take a rectangular plate of tourmaline, cut so that one of its faces is parallel to the axis of the crystal.If a beam of electrical or direct sunlight normal to the plate, the rotation of the plate around it does not cause changes in the intensity of light that passes through it.There is a feeling that the transmitted light to partially absorb tourmaline and bought a light green color.Nothing else happens.But this is wrong.The light wave acquires new properties.
They can detect if the light beam passes through a second crystal of tourmaline, which is parallel to the first.At the same direction as the crystal axes of the two curious anything happens, only a beam of light is increasingly attenuated due to absorption, passing through the second crystal.But with the rotation of the second crystal, if this first leave motionless, found an interesting phenomenon called "extinction of light."In the process of increasing the angle between these two axes decreases the saturation of the transmitted light beam.When the two axes are perpendicular with respect to each other, the light can not pass at all.He will be completely absorbed by the second crystal.How is this?
transversality of light waves
From the description of the facts, as shown above, must:
1. Firstly, the light wave that goes from the light source completely symmetric with respect to the direction in which the propagation takes place.At the back of the crystal around passing a beam of light at the first of the experiment did not change its intensity.
2. Secondly, the wave emerging from the first crystal will not have axial symmetry.The intensity of the transmitted light through another crystal depends on its rotation.
longitudinal waves differ complete symmetry with respect to the direction of propagation.Fluctuations longitudinal waves occur along this direction, and this oscillation is the axis of symmetry of the wave.It is clarified however experience with the rotation of the second crystal, assuming a longitudinal wave beam is not possible: the - transverse waves.
can fully explain the experience, making two assumptions:
Assumption number one is directly related to the light: the light waves - transverse waves.But in the incident beam from the light source contains the light waves of different oscillation directions are perpendicular to the direction in which this wave is propagated.In this case, considering this assumption, one may conclude that the wave beam is axially symmetrical, at the same time being transverse.For example, waves on the water surface do not have such symmetry, because the fluctuations of the water particles occurs exclusively in a vertical plane.
waves of light with variations in different directions, which are perpendicular to the direction of propagation are called natural.This name is justified because under standard conditions different light sources to create just such a wave.This assumption explains the results of the first of the experiment.Rotation tourmaline crystal does not change the saturation of the transmitted beam of light, because this incident wave has an axial symmetry, despite the fact that she - a transverse wave.
second assumption refers to the crystal.Tourmaline has the property of flowing waves of light with oscillations that occur in a specific plane.This light is called polarized (or plane-polarized).It differs from the natural, unpolarized.
This assumption explains the second experiment.From the first crystal of tourmaline out of plane polarized light (wave).At the intersection of the crystal an angle of ninety degrees wave can not pass through the second one.If the angle of the crossing of another, it will be held oscillations whose amplitude is equal to the projection of the amplitude of the wave passing through the first plate in the direction of the axis of the second.It also is evidence of the theory that light waves - transverse waves.
