In the figure on the left below, unpolarized light is sent through a system of t
ID: 2095572 • Letter: I
Question
In the figure on the left below, unpolarized light is sent through a system of three polarizing sheets. The angles ?1, ?2, and ?3 of the polarizing axes of the sheets are measured counterclockwise from the positive direction of the y axis (they are not drawn to scale). Angles ?1 and ?3 are fixed but angle ?2 can be varied. The figure on the right gives the intensity of the light emerging from sheet 3 as a function of ?2. (The scale of the intensity axis is not indicated.) What percentage of the light's initial intensity is transmitted by the three-sheet system when ?2 = 90
Explanation / Answer
From the graph Intensity I is zero when ?2= 140 DEGREES.For the intensity to be zero theangle between the two polarisers must be 90 degrees.Then ?2 -90 = ?1 Then 140 - 90 =?1 Thus?1 = 50 deg . Now consider the case ?2 = 90deg As ?1 is fixed then ?1 =50 deg Then angle between the two polarisers is ?? = 90-50 = 40 deg Then the intensity through second polariser I2=I1cos2?? I1= Intensity of light through the first polariser= Io/2 ThenI2=(Io/2)cos2?? fraction of light is f = I2/Io =(1/2)cos2??=(1/2)cos(2*40) = 0.086 = 8.6%
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