8.3 Production and Detection of Plane Polarized Light
The light emitted by an ordinary incandescent bulb is unpolarized, because its electrical vibrations are randomly oriented in space as shown in Fig. 8.2.
If unpolarized light is made incident on a sheet of polaroid (polarizer), the transmitted light will be plane polarized. If a second sheet of polaroid (analyzer) is placed in such a way that the axes of the two polaroids shown by straight lines drawn on them are parallel (Fig. 8.5-a), the light is transmitted through the second polaroid. If the second polaroid (analyzer) is slowly rotated about the beam of light as axis of rotation, the light emerging from the second polaroid gets dimmer and dimmer and ultimately disappears when the axes become mutually perpendicular as shown in Fig. 8.5(b), the light reappears on further rotation and becomes brightest when the axes are again parallel to each other.
This experiment proves that light waves are transverse waves. If the light waves were longitudinal, they would never disappear even if the two polaroids were mutually perpendicular.