Question

by which techniques light is polarized?

Answer 1

selective absorption
reflection from different surfaces
refraction through crystals
scattering by small particles

Answer 2

with the use of a polaroid filter.polaroid filters are made of a special material that is capable of blocking one of the two planes of vibration of an electromagnetic wave.in this sense ,a polaroid serves as a device that filters out one half of the vibrations upon transmission of the light through the filter. when unpolarized light is transmitted through a polaroid filter,.it emerges with one half the intensity and with vibrations in a single plane then emerges as polarized light.