Diffraction Grating
Diffraction of light occurs when a light wave passes by a corner or sharp edge or slit that is of physical size equal or even smaller than light’s wavelength. Diffraction grating is an optical component which consists of a periodic arrangement of equidistance slits of large number of parallel equidistance lines. When light is shine upon these grating, diffraction patterns are produced on the screen (VIBGYOR). Wavelength of lights are given by
\[ \lambda = \frac{2.54 \sin \theta}{nN} \]where θ is the diffraction angle, n is the diffraction order, N is the number of parallel lines per inch in grating element (LPI)
Procedure
- Switch on the Mercury Source. Level the spectrometer by using the spirit level. Get a fine beam of white light by adjusting the collimator and eyepiece of the spectrometer.
- Before performing the experiment, it is mandatory to set the instrument to normal incidence position as shown in the figure below.
- Place the diffraction grating on the grating stand. Focus the eyepiece on the zero order of the diffracted white light. Next rotate the telescope toward right such that it makes an angle 90° with the collimator. Without disturbing the telescope adjust the grating to get the view of zero order white light and match with the cross wire.
- Now move the rotating table base at an angle 45° toward the collimator. Bring back the telescope in line with the axis of collimator and focus on the white light. Now the instrument is said to be in Normal Incidence position
