Intensity of light before and after passing through one plane-polarized filter?

[Gauss44]

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Nonpolarized light passes through one plane polarized filter. What is the intensity of the light which has passed through the filter compared to nonpolarized light?

If it is half the intensity, why?

As an aside, is it correct English to say unpolarized or nonpolarized? Or both?

 

[milski]

Non polarized means that it is a combination of wave polarized randomly in all directions. Since the intensity for a polarization at angle θ is cos²θ times the intensity, the total intensity of the light after the filter is the average of cos²θ for all angles between 0 and 360 degrees which is 1/2.

The typical usage is non-polarized although m-w.com does have unpolarized too. Unpolarized implies that it was polarized at some point but it's not now, which is probably why it's not usually used.