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An unpolarized beam of light is incident on a stack of ideal polarizing filters.

ID: 2015280 • Letter: A

Question

An unpolarized beam of light is incident on a stack of ideal polarizing filters. Find the fraction by which the transmitted beam's intensity is reduced in the following three cases.
(a) Three filters are in the stack, each with its transmission axis at 43.7° relative to the preceding filter.


(b) Four filters are in the stack, each with its transmission axis at 30.4° relative to the preceding filter.


(c) Seven filters are in the stack, each with its axis at 16.6° relative to the proceeding filter.

Explanation / Answer

It is Known by the Malus law , we have a relation between , intensity of the incident light to transmitted light , If filter makes an angle    is given by (a) I = Io cos2    where represents transmission axis makes relative to preceding filter . When , the light incident on the first filter the transmitted light intesity becomes to Half thus, I1 = Io/2              I2 = I1 cos2               I3 = I2 cos2    thus, we can simply writen as        I3 = Io /2 (cos2)(cos2 )      for the fraction :        I3 / Io = (cos2 )(cos2 ) /2                   = (cos2  43.7 )(cos2 43.7 ) /2                   = 0.136 (b)         simillarly       For , four filters            we have ,                            I4 / Io = (cos2 )(cos2 ) )(cos2 ) /2                          = (cos2  30.4 )(cos2 30.4 ) )(cos2 30.4 ) /2                          = 0.2058 (c)              For , Seven filters,              we have ,                  I7 / Io = (cos2 )(cos2 ) )(cos2 ) (cos2 )(cos2 ) )(cos2 )/2                              = (cos12 ) /2                              = (cos12  16.6 ) /2                              = 0.2999 (c)              For , Seven filters,              we have ,                  I7 / Io = (cos2 )(cos2 ) )(cos2 ) (cos2 )(cos2 ) )(cos2 )/2                              = (cos12 ) /2                              = (cos12  16.6 ) /2                              = 0.2999             
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