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A monochromatic beam falls on a reflection grating with period d = 1.0mm at a glancing angle alpha_(0) = 1.0^(@). When it is diffracted at a glancing angle alpha = 3.0^(@) a Fraunhofer maximum of second order occurs. Find the wavelength of light. |
Answer» Solution : Tha path difference between waves REFLECTED at `A` and `B` is `d(COS alpha_(0) -cos alpha)` and maxima `d(cos alpha_() - cos alpha) = k lambda, k = 0, +- 1, +- 2,………` In our case, `k = 2` and `alpha_(0), alpha` are smalll in radius. Then `2lambda = d((alpha^(2) - alpha_(0)^(2))/(2))` Thus `lambda - ((alpha^(2) - alpha_(0)^(2))d)/(4) = 0.61 MU m` for `alpha = (3PI)/(180), alpha_(0) = (pi)/(180), d = 10^(-3)m` |
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