Virtual Lab No. 3:  The Visible Spectrum of Hydrogen.

Introduction

In this lab we will see how Bohr's model of the hydrogen atom can account
for its observed spectrum.  Your goal is to find the orbit transitions
that produce the four visible lines in the spectrum for both the emission
and absorption cases.  The applets for this lab can be found at the
links  http://phys.educ.ksu.edu/vqm/html/emission.html
for the emission spectrum, and  http://phys.educ.ksu.edu/vqm/html/absorption.html
.  Instructions for using the applet are included in this link. 
For those who don't want to calculate orbit energies themselves, you can
determine these by using the applet located at  http://home.a-city.de/walter.fendt/phe/bohrh.htm
. The energy of the electron in the currently selected orbit is given in
the lower right hand corner of the applet window.  Values in joules
and electron volts are given, you will  need the latter unit value
for this lab.

Procedure

1. 
   The first step is to construct a table showing the electron energy in each
   of its possible orbits. Although in reality there are an infinite number
   of possibilities, to investigate the visible spectrum we need only consider
   values from n = 2 to n = 6.  The energy of the electron in each orbit
   can be found either using the formula ,
   or by using the Bohr
   theory of hydrogen applet.














































Principal Quantum Number n	Electron Energy (in eV)
n = 1
n = 2
n = 3
n = 4
n = 5
n = 6




2. 
   Next, load the emission
   spectrum applet. This will open in a new browser window. Move the mouse
   over one of the spectrum lamps; when you do so, the name of the material
   in the lamp will appear next to it.  Select the hydrogen lamp by clicking
   and dragging it to the spectrum lamp sockets. When the lamp is placed in
   the socket, the visible part of the hydrogen spectrum will appear at the
   top of the applet window.



3. 
   Follow the instructions in the applet to add each of the energy levels
   in your table to the energy level diagram in the applet. Since the graph
   scale is fairly coarse, you won't be able to match them exactly, but try
   to get as close as you can.



4. 
   With energy levels in place, you are ready to begin experimenting with
   transitions. When you enter a transition in the diagram, the spectral line
   to which it corresponds will appear in the section below the hydrogen spectrum,
   if its wavelength lies in the visible range, otherwise, nothing will happen.
   If you need to remove a transition, you can do so by dragging it off the
   graph.



5. 
   Once you have obtained all four of the visible lines in the hydrogen spectrum,
   complete the table below.












































Spectral Line	Starting Orbit Number	Ending Orbit No.
Red
Blue
1st Violet
2nd Violet




6. 
   Next, load the absorption
   spectrum applet. Add the electron energy levels to it in the same fashion
   as for the emission applet. Experiment with transitions until you duplicate
   all the absorption lines and complete the table below.














































Absorption Spectrum Transition for Hydrogen

Spectral Line	Starting Orbit No.	Ending Orbit No.
1st
2nd
3rd
4th






Questions


1.  Do you see any patterns in the transitions that generate the emission
spectrum of hydrogen?  If so, what are they?

 

 

 

 

 


2. How do the transitions that generate the absorption spectrum compare
with those that generate the emission spectrum?