What is the effective (mean) wavelength is given by
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lamdamean =1+(5/6)(Deltalamda/lamda2)
+(deltalamda/lamda)4
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=1+(0.833)(0.35/1.35mm2)+(0.35/1.35)4
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= 1+0.833(2.592*10-4)+(4.426*10-3)
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= 5.64*10-3m
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=5.64mm