Figure 1: The Zeeman Effect experimental apparatus.
Apparatus
Equipment
Personnel
The Cd-Hg lamp gives off some ultraviolet radiation. Avoid looking directly at the lamp.
The lamp becomes hot when in operation.
Apparatus
THE LUMMER-GEHRCKE PLATE IS LOOSELY POSITIONED IN THE OPTICAL SYSTEM - DOT NOT TILT OR JOLT THE OPTICAL SYSTEM.
Increase and decrease voltage applied to the magnet fairly slowly; avoid sudden changes in the current; do not just turn it off but reduce voltage to zero and then turn off.
Handle Cd-Hg lamp with care; do not touch the bulb itself.
Handle optical components by edges; do not touch optical surfaces.
Magnetic field calibration. A gaussmeter is used to obtain a calibration of magnetic field versus voltage applied to the magnet, B versus V. An iron magnet may show significant hysterisis effects, and the following cycling procedure should be observed when establishing a magnetic field for these experiments. Always make changes in the voltage fairly slowly.
Run the voltage from zero up to its maximum value, a but above 12 V. Then run the voltage back down to zero. Finally increase the voltage from zero to the desired value. If you inadvertently run the voltage up beyond the desired value, you should repeat the cycle: turn V up to maximum value, back down to zero, and finally up to the desired value.
In order to calibrate the magnet and verify the reproducibility of a desired field, obtain the following data. Cycle the magnet to maximum V and then to zero. Beginning with V = 0 obtain data for B versus V up to the maximum V possible, using steps of about 1 V. Then obtain data for B versus V as you decrease the voltage from the maximum value back to zero. Finally, obtain two more points by running the voltage up to about 8 V and 10 V. Upon completion of data taking for these final two points, run the voltage up to its maximum value and then down to zero, which leaves the magnet ready to begin your Zeeman effect experiments.
Present the data as a plot of B versus V, distinguishing between points taken while increasing the voltage and while decreasing the voltage. Also, distinctly show the final two points, which is indicative of the reproducibility of a magnetic field using the suggested cycling procedure. You may notice that for this particular magnet under the conditions investigated here, there is no noticeable hysterisis effect.
Connect the points of your B versus V curve corresponding to increasing V’s by a smooth curve. Use this curve to obtain magnetic field values for the Zeeman effect experiments. The gaussmeter will no longer be used.
Select three fringes for observation; probably the more widely separated fringes will yield better data. With no magnetic field applied, measure the separation between the outer fringes, the distance 2a. The indicator gauge attached to the optical system is used for the measurements. Only a ratio of distances will be used in computations. Hence no calibration of the gauge is needed.
When the magnetic field is applied, the splitting of the central line will be studied. For the lines of interest here, the splitting will be symmetrical, and the distance 2s is measured.
Polarization of the light emitted when the field is applied may be studied by use of the plane polarizer and the quarter-wave plate. In looking for circular polarization, the quarter-wave plate must be closest to the light source. The quarter-wave plate is attached to the mount for the Lummer-Gehrcke plate, and the plane polarizing filter is attached to the telescope. When making observations perpendicular to the magnetic field, one expects plane polarization to be of interest, with polarizations either parallel to the magnetic field or perpendicular to the magnetic field. When making observations along the axis of the magnetic field (light emerging through the hole in one of the magnet pole pieces), one expects circular polarization to be of interest. You do want to notice that some lines are circularly polarized in one sense while others are polarized in the other sense. However, we will not attempt to get straight which is denoted right and which is denoted left circular polarized.
Insert the red filter and attached lens on end of L-G plate assembly next to light source. Select three fringes and measure 2a. You can decide whether use of a plane polarizing filter is useful in blocking out the undisplaced line. Measure the splitting 2s as a function of voltage applied to the magnet coils over a range of about 4 V to the maximum of about 12 V, in steps of 1 or 2 volts.
Make a table showing V, B, 2s, and Δλ. Plot Δλ versus B. B values for the V values you have used are obtained from the calibration curve made in part 1. The index of refraction to be used for the Lummer-Gehrcke plate is obtained from the graph of index of refraction of quartz versus wavelength. This graph is located in the supplemental section.
Investigate the polarization of the displaced lines and the undisplaced line and comment on the results in the report. The main effect should be plane polarization, although instrumental effects may suggest (spurious) small circular polarization effects.
Repeat work similar to that conducted in part (2), with reorientation of the magnet. Here you will not want any polarizing filter or quarter-wave plate in the system while measuring the splittings. You should find circular polarization of the lines when the magnetic field is applied. Plot Δλ versus B on the same axes as used for part (2). Ensure that the points for the two different experiments are distinguishable.
Replace the red filter and lens with the green filter and lens. The green filter and lens must be propped up between the magnet and the L-G plate assembly. Study the expected Zeeman patterns on the attachment and attempt to interpret your polarization observations, with both orientations of the magnet. This apparatus is not intended to be suitable for making good studies of the anomalous Zeeman effect because the resolution of the L-G plate is inadequate to achieve clean separations of the Zeeman components. In your report discuss your polarization observations as best you can.
Select one (or more) of the following configurations for this study.
A. Observe light emitted (through hole in magnet pole piece) parallel to B. No polarizing filter or quarter-wave plate is used. Circular polarization is expected, but use of a filter will destroy the symmetry of the splitting and upset measurements of the splitting 2s.
B. Observe light emitted perpendicular to B and polarized parallel to B. A plane polarizer is used to eliminate the light polarized perpendicular to B.
C. Observe light emitted perpendicular to B and polarized perpendicular to B. A plane polarizer is used to eliminate the light polarized parallel to B.
The same general procedure is used as was employed for measurements of the normal Zeeman effect. The limited resolution of the apparatus makes precise measurements impossible, of course, but rough measurements are possible. Three fringes are selected, and 2a is measured. With application of the magnetic field, measurements of the splitting, 2s, are made for 3 or 4 values of the field. Except for configuration (B), the "line" displaced to one side of the zero-field position should show structure, as opposed to being a single line. However, the limited resolution of the apparatus probably gives the appearance of a single, albeit fuzzy, line.
Before commencing quantitative measurements of the splitting, qualitatively investigate the appearance of the splitting as a function of field and determine a range of field values (i.e., voltages) over which decent measurements can be made. There will be some minimum field at which the splitting becomes measurable. For configurations (A) and (C) you will probably find some maximum field, beyond which lines from adjacent fringes overlap to such an extent as to render further measurements impractical.
Present the results as you did for observations of the normal Zeeman effect, viz. prepare a table showing V, B, 2s, and Δλ; plot Δλ versus B. Prepare a separate graph for this part; if you do more than one configuration, you may put all the plots on the same graph, but clearly distinguish between the configurations.
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