7. When initially-unpolarized light passes through three polarizing filters, each oriented at 45 degree angles from the preceding filter, of the initial light passes through the last filter.

Explanation:

Let the intensity  of unpolarised light be I₀ . After passing through the first polarising filter , the intensity  is I₀ / 2 .

After second filter , the intensity  will be  I₀ / 2 x cos²45 =  I₀ / 4

After third filter , the intensity will be I₀ / 4  x cos²45 = I₀ / 8 .

So,

1 / 8 the of initial light passes through the last filter .

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