![]() I,e resolving power of grating is proportional to number. Minima due to wavelength λ in the direction $θ_n$ + $dθ_n$ is given by Therefore dividing equation (2) by equation (1) This is the condition for the absent spectra in the diffraction pattern If a b i.e., the width of transparent portion is equal to the width of opaque portion then from equation (3) n 2m i.e., 2nd, 4th, 6th etc., orders of the spectra will be absent corresponds to the minima due to single. Maximum due to wavelength λ+dλ in the direction $θ_n$+ $dθ_n$ is given by We know, in grating equation for maxima is (a+b) sinθ = nλĪnd minima is N (a+b) sinθ = mλ (m = nN ☑ ) ![]() P1 is the nth principal maximum of wavelength λ at an angle θ_n and P2 is nth principal maxima due to wavelength λ + dλ at an angle $θ_n$+ $dθ_n$Īccording to Rayleigh`s criterion, two wavelengths will be just resolved if principal maxima of λ + dλ in the direction $θ_n$+$dθ_n$ falls on the first minima of λ in the direction $θ_n$ +$dθ_n$ let the beam of two wavelengths λ and λ+dλ is incident normally on the grating (1)m d(sin+sin) m d ( sin + sin ) m is an integer value describing the diffraction (or spectral) order, is the light’s wavelength, d is the spacing between grooves on the grating, is the incident angle of light, and is the diffracted angle of light leaving the grating. Let AB be the plane diffraction grating of grating constant (a+b). This is measured by λ/dλ where dλ is the smallest difference between two wavelengths an λ is mean wavelength. Resolving power of grating is defined as the capacity to form separate maxima of two wavelength which are very close to each other. The history of diffraction gratings 1, 2 can be traced back to 1785 when Rittenhouse made the first known transmission grating by winding human hair between. One of the important property of grating is ability to separate spectral lines which have nearly same wavelength. The resolving power of an instrument is ability of the instrument to produce separate image of object which are very close to each other.Īccording to Rayleigh`s criterion, two-point sources are resolvable by a optical instrument when the central maxima in the diffraction pattern of one falls over the first minimum due to other and vice versa. ![]() An optical instrument is said to be able to resolve two-point objects if their corresponding diffraction pattern is distinguishable. ![]()
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