Aim of the experiment
Apparatus
Spectrometer, sodium vapor lamp, mercury vapor lamp, watch maker eye glass and small flash lights.
Abstract
This is the phenomenon where atoms are excited and emit light of various wavelengths. These lines which are colored with dark fringes between them are known as atomic spectra. All elements have distinct set of spectral lines. It is this unique spectrum associated with certain distinct element. The atomic spectra of various elements of investigation will be studied in this experiment using a diffraction grating mounted on a spectrometer. The atomic transitions of various elements under investigation will be used to calibrate the line of spacing of the grating. The elements which were under investigation included hydrogen. The apparatus was put in place and a certain procedure was followed to make the general conclusions. The lab technician was always with us to ensure that the procedure was correctly followed.
Background Information
Hydrogen atoms consists of a single proton nucleus surrounded by an electron. From the laws of quantum mechanics, an electron is only allowed only certain energy levels dictated by the principle quantum number. When the electron drops from a level denoted by En to a lower energy level Em it emits a photon of a known frequency. The light emitted from the hydrogen therefore consists of a number of discrete spectral lines of wavelengths given by the equation below.
Where RH is the Rydberg constant for hydrogen. This number can be calculated theoretically from the results to obtain RH = 1.0967758 Exp7 m-1. This number is always true for vacuum wavelengths but in relation to air the following equation comes into play.
λ=naλair
Where the character na is the refractive index of the air. The transitions to the m= 2 level are in the visible and near ultraviolet region of the spectrum and are said to be the Balmer series of the spectral lines. The red line is the H alpha line, the green is the H beta line while the blue line is known as the H gamma line. The rest of the lines are violet or ultra violet which form the Paschen and Lyman series as well as the Pfund series
Procedure
Set the apparatus as shown in the figure below
- Rotate the telescope so that it looks directly into the collimator at the image of the slit. Observe the central band n = 0, the zero order, slit image. A thin bright image can be easily observed when the width of the slit is reduced.
- With the vertical cross hair in line with the slit of the image, ensure that the arm of the telescope is aligned accordingly. For fine image adjustment of the crosshair, ensure the telescope is locked into position.
- Measure the angular position of the telescope arm on the graduate scale using the watchmaker eyeglass to read. Observe that the reading made on the vernier scale accuracy can be adjusted to one minute of the arc.
- With your right eye, move to the right of the telescope. Looking into the diffraction grating, move backwards and forward to observe the first order n=1 image of the slit.
- Lock the telescope using the locking screw. Align the image with crosshair using tangent screw. Measure and record this position as the first order whose n=0
- Use the above procedure for the spectral analysis of mercury and sodium.
Results
For hydrogen the spectral lines were as shown in the figure below.
Discussion
Hydrogen forms three distinct lines of different colors. These lines are red for the H alpha line, green for H beta line and violet or ultra violet for the H gamma line.
Conclusion and summary
References
Atomic Absorption and Emission Spectra. Retrieved from http://csep10.phys.utk.edu/astr162/lect/light/absorption.html
Science Trek, Quantum atom. Atomic Spectra. Retrieved from http://www.colorado.edu/physics/2000/quantumzone/lines2.html
Dietrich Zawicha Atomic Spectra. Retrieved from https://www.itp.uni-hannover.de/~zawischa/ITP/atoms.html
Atomic Spectra, Hydrogen Spectrum. Retrieved from http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/atspect.html
