SCIENCE,TECHNOLOGY & SOCIETY Polaroid sunglasses
Light that is reflected from a glass or a water surface is partially (horizontally) plane polarised. Polaroid sunglasses can be used to reduce this glare. As illus- trated in Fig 14.29, the blue waves (representing light reflecting off surfaces we wish to view) are oriented in the same direction as the polarising lenses and, therefore, are passed through the Polaroid. In contrast, the orange wave represents glare, which is parallel to the surface of the road.
Since the orange wave is perpendicular to the Polaroid lenses it is successfully blocked. The benefits of using Polaroid glasses are shown in the photos below. On a bright sunny day, it may be difficult to see through a window. Using Polaroid glasses allows you to see through that surface.
Light waves vibrating perpendicular to the road
Light waves vibrating parallel
to the road Fig 14.29: Polaroid sunglasses Unpolarized Polarized
glare
glare reduced
Polaroid sunglasses reduce the amount of glare coming off the table
Stress polarisation
Engineers can test the internal stress of a transparent material by passing a beam of polarised light through the object and viewing it through a Polaroid lens. The stressed material can turn the plane of polarisation of the incoming beam of light. The degree to which the plane of polarisation is turned depends on the colour of the light and the stress or characteristic of the material at any given point. When this polarised light is viewed through a Polaroid lens, it gives rise to an array of colours. Engineers can analyse these colours to test for stress by making plastic models of bridges, etc.
A hard transparent plastic shows the effects of stress polarisation
