![]() From the figure, we note that the path difference’ δ ‘ between rays from any two adjacent slits is equal to d sin θ. However, for some arbitrary direction θ measured from the horizontal, the waves must travel different path lengths before reaching point p. The waves from all slits are in phase as they leave the slits. Each slit is produced diffraction, and the diffracted beams interfere with one another to produce the final pattern. The pattern observed on the screen is the result of the combined effects of interference and diffraction. A converging lens brings the rays together at point P. A plane wave is an incident from the left, normal to the plane of the grating. A section of a diffraction grating is illustrated in the figure. For example, a grating ruled with 5000 lines/cm has a slit spacing d=1/5000 cm=2.00×10 -4 cm. Gratings that have many lines very close to each other can have very small slit spacing. A reflection grating can be made by cutting parallel lines on the surface of refractive material. The space between the lines is transparent to the light and hence acts as separate slits. A transmission grating can be made by cutting parallel lines on a glass plate with a precision ruling machine. The space between lines acts as slits and these slits diffract the light waves thereby producing a large number of beams that interfere in such a way to produce spectra. It consists of a large number of equally spaced parallel slits.” Its working principle is based on the phenomenon of diffraction. “The diffraction grating is a useful device for analyzing light sources.
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