Experiment #4 THE DIFFRACTION GRATING Purpose: To determine the grating constant and rulings of a diffraction grating Apparatus: Apparatus Spectrometer Diffraction grating Grating support Helium discharge lamp Serial/Model Number Uncertainty Procedure: 1. Use the helium discharge tube as your source. 2. Place the grating on the spectrometer table. 3. Determine and record the central position. 4. Determine the angular positions for all the spectral lines of the helium spectrum. on both side of the central position. Use the first order of diffraction only. Drawing: Light source Support grating Telescope Colimating scope Sample Calculations: pg. 2 The Spectrometer (side view) Experiment No. 4 Equipment, serial numbers and uncertainties Spectrometer sn: 1141F440 unc: ±0.5'; Diffraction grating sn: 0611039004 unc: N/A; Grating support sn: 0606142 unc: N/A; Helium discharge lamp sn: 1142F440 unc: N/A Violet 172°-18" Left Angle ("or") (measured value) Right Angle (or ') (measured value) 187°-45' Wavelength Blue 171°-55' 188°-9' 447.15 nanometres 471.31 nanometres Green 2 171°-30' 188°-31' 492.19 nanometres Green 1 171°-22' 188°-42 501.57 nanometres Yellow 169°-55' 190°-11' 587.56 nanometres Red 2 168°-30' 191°-33' 667.81 nanometres Red 1 167°-51' 192°-15' 706.52 nanometres Central position 180°-0' Table of calculated results Violet Blue Green 2 Green 1 Yellow Red 2 Red 1 Left Angle (°) Grating constant (m) Right Angle (°) Grating constant (m) Average grading constant (m) Ruling (lines/m) Error analysis: Error calculations: (remembers to keep your calculations neat and orderly and remember to number added pages 5a,5b, 5c, etc.) pg. 5 Error analysis (cont): Possible sources of errors for this experiment are: