Estimating the wavelength of light using a double-slit and a plane diffraction grating

... Title Estimating the wavelength of light using a double-slit and a plane diffraction grating Objective To project a Young's interference pattern on a screen and make measurements to estimate the wavelength of light To estimate the wavelengths of the different colours of the spectrum produced using a fine diffraction grating Apparatus Instrument Descriptions 1 double slit Mounted on a large cardboard 1 translucent screen Ground glass 1 Compact light source With vertical filament 1 Low voltage power supply ------------------------------------------------- 1 Magnifying glass ------------------------------------------------- 2 metre rule 100 cm 1 vernier caliper Smallest division 0.1mm 1 diffraction grating 3000 lines per cm 1 ray-box Without lens and slit plate Theory Using a double-slit In the Young's double slit experiment, two rays through the slits interfere to give the interference pattern. Bright fringes occur at positions where constructive interference occurs (Fig.1). The path difference from the slits at an angle ? is a multiple n of the wavelength ?, i.e. a sin ?=n?, where n=1,2,3... is known as order number. For small value of ?, Sin?= tan?= s/D Where s is the distance of the

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