POLARIZATION OF LIGHT

[Music] so [Music] it's difficult to see beyond the glare of approaching headlights but polarized filters on an oncoming car and seen through a polarized screen can reduce glare and reflection rapidly and dramatically rotating polarized filters are often used in photography let's see how such a filter reduces the reflection from a shop window a polarized filter can extinguish the reflection or restore it photographers also use polarized filters to reduce the diffused light of the sky for richer colors and pictures in order to investigate polarized light let's use this balcony door on a stage setting note the reflection in the clear glass of the door and in the polish table why doesn't the reflection in the door appear in the table top let's see from every point of the house across the street parallel light rays fall on the window these light rays are reflected by the window and create the image that we see now let's look at one single light ray light behaves like a wave the light waves oscillate in many directions perpendicular to the direction of the ray but when the oscillations fall on the window part of them pass through the glass while some are reflected the oscillations of the reflected light are parallel to the plane of the window light consisting of oscillations in only one direction is called polarized light these oscillations are not parallel to the plane of the table they are not reflected but absorbed this is why despite the other reflections the reflection from the window does not appear on the table but tilt the table to a plane closer to the plane of the glass and a reflection begins to appear and then it disappears window glass and table tops are awkward to move so we will use ordinary glass at an angle an artificial light to examine polarization for further demonstration any sheet of plain glass will do but we must ensure that is placed at the correct angle in the path of the light if more glass sheets are applied the effect is increased several glass sheets tied together work in a similar manner using this system it can be observed that both the reflected light and the transmitted light are polarized with several sheets of glass and a frame let's construct a simple device to view polarization phenomena when turned to the correct position it does not permit the reflected polarized light to pass through [Music] so [Music] in nature there are many transparent materials which due to their inner structure polarized light such as this calcite crystal the light passing through this crystal is divided in two not only are both rays polarized but their polarization directions are perpendicular the tourmaline crystal is also doubly refracting however it differs from the calcite crystal because it absorbs one of the polarized rays and only allows the other to pass through today large size polarizing material is produced in an artificial way the essence of this production is that by stretching synthetic material a chain molecular structure is turned into parallel grid layers these are then dyed the grid structure behaves like a doubly refracting crystal but the dye absorbs one of the rays in the same way as the tourmaline crystal this sheet lets the oscillations through in only one direction thus polarizing light we can see clearly through two sheets when they are in identical positions after a 90 degree turn the second sheet does not let the light pass through together the pair makes a polar filter glass and other material have invisible internal stresses heat or other physical energy can cause explosions or other breakage [Applause] with glass this usually occurs on the cooling rack in the manufacturing plant valuable technical glassware where the risk of accidental explosion should be reduced can be examined for internal stresses by means of polarized light through polarized glasses points of uneven stress are rapidly identified this optical stress analysis is used in many technical fields for example polarized light can be used to study load pressures building structures carry heavy loads and stresses in order to investigate these forces a model of the base is produced from a plastic material this equipment is used to examine stress in the model when loaded the density and size of the color rings reveals the site and extent of the stresses the discoloring arising in a model of a crane hook assist engineers in designing the correct shape for such hooks if the stresses on a railway bridge are to be examined another model is made from transparent gelatin the greatest stress is where the model becomes darkest under polarized light the play of the forces of moving loads can also be observed here is a rubber membrane under polarized light colors begin to appear when tension is applied these synthetic rulers made by an identical process show the same color patterns indicating similar stresses under the microscope thin rock particles illuminated by polarized light reveal details of their inner composition useful to geologists in the study and identification of minerals from the earth and outer space layers of folded cellophane separate into a rich and brilliant kaleidoscope of color under polarized light a terrace of increasing layers of transparent cellophane is transformed into a vivid color display [Music] as is this mounted butterfly [Music] in geometric form [Music] the polarization of light although it can be a source of lovely form and color is primarily a useful and important phenomenon to scientists builders artists and engineers [Music] [Music] do [Music] you