Why is the intensity of polarized light half of the intensity of unpolarised light?

Answer 1

This is actually a huge question and not always true.

Polarized light is "lined up" by frequency, the filter used to do this does not allow for incoherent light waves of different frequencies.

Moving into the difference in polarized and non-polarized waves of the same frequency; by polarizing the waveform, the elimination of perpendicular radiation causes the radiance to be reduced. Think of having light waves making an X coming toward you (so that you can see the X); polarizing would allow only 1 leg of the X or a / to get through the filter.

This is really a simply and incomplete answer but I hope that it helps.

Answer 2

I am not sure what you mean by "unpolarised" light, as all EMF radiation has inherent polarization. Are you referring to the random polarization that is generated by most common incoherent light sources?

Perhaps you are talking about using a "polarizing" filter on a random polarized source. The comparative loss in intensity is due to the filters inability to pass EMF radiation of certain orientations. The loss is a characteristic of the filter you are using.

Answer 3

Unpolarised light will have electric fld distributed randomly in all directions in the plane normal to the direction of travel of the wave. Taking the components of the fld. along and normal to the polarising axis of the polariser, the energy will be equally divided in the two components. Since the polariser allows only one of these components, the polarised light will have half the intensity of the original light.

Answer 4

because some light is stopped by polariser.