Main Page/PHYS 3220/Excitation Potentials - Revision history

Gloria at 16:51, 30 October 2018

2018-10-30T16:51:27Z

Gloria at 16:48, 30 October 2018

2018-10-30T16:48:10Z

Gloria at 16:45, 30 October 2018

2018-10-30T16:45:34Z

Gloria at 17:56, 11 October 2018

2018-10-11T17:56:52Z

Gloria at 17:49, 11 October 2018

2018-10-11T17:49:14Z

Gloria at 17:47, 11 October 2018

2018-10-11T17:47:59Z

Gloria at 17:30, 10 October 2017

2017-10-10T17:30:30Z

Mgeorge at 19:40, 26 August 2013

2013-08-26T19:40:07Z

Mgeorge at 14:30, 7 November 2012

2012-11-07T14:30:54Z

Mgeorge at 14:29, 7 November 2012

2012-11-07T14:29:33Z

@@ Line 51: / Line 51: @@
 <p>For this experiment, we require voltage sweep from 0 to 35 V which is isolated from ground. Most function generators you find around the lab cannot give such large amplitudes, so we will need to use a power supply that will be controlled by a ramp generator.  Two power supplies (GW Instek GPS-1850D) connected in series will be controlled by a function generator (model:ASFG-2R) to generate the voltage sweep from 0 to 35 V. Note that neither output of the power supply is referenced to ground. In order to view the amplifier waveform, we will use an oscilloscope. Many oscilloscopes are designed in such a way that the outer conductor of its input jacks are automatically connected to ground. This will not work for our situation, since we need the sweep voltage to be unreferenced to ground. Therefore, we will need to operate the scope in a more advanced manner to observe the sweep. We will take the negative output of the power supply and connect it to the inner pin of CH2, and the positive output of the power supply will be attached to the inner pin of CH1 on the scope. Using the MATH function on the scope, we can display CH1-CH2, which is our sweep voltage of interest, without having connected anything to the outer conductor of the oscilloscope and forcing a ground in the circuit where one is not desired. Note, if you cannot attain a 0 - 35V ramp voltage without distortion, lower the ramp frequency. </p>
 <ol>
-<li> Turn on the sweep generator and select a triangle waveform.</li>
+<li> While observing the CH1-CH2 MATH signal as described above, adjust the amplitude and offset to get a 0 to 35 V ramp signal if needed.</li>
 <li> Set the frequency to be a few tens of Hz. (You may want to try changing this value later).</li>
 </ol>
@@ Line 71: / Line 69: @@
 <h3>Saving the Scope Traces</h3>
-<p> Use a USB stick to save the math signal (red trace) and Ch. 4 (amplifier output).
+<p> Use a USB stick to save the math signal (red trace) and Ch. 4 (amplifier output).</p>
 <!--<p>Using the computer to the computer to the right of apparatus.

@@ Line 70: / Line 70: @@
 <h3>Saving the Scope Traces</h3>
 <!--<p>Using the computer to the computer to the right of apparatus.
@@ Line 82: / Line 84: @@
 <h2>Measurements</h2>
-<p>Find as many values as you can of the excitation energy ("excitation potential") from your record. Repeat these measurements for 10 different temperature values. Perform a full error analysis and compare your results with the expected values.</p>
+<p>Find as many values as you can of the excitation energy ("excitation potential") from your record. Repeat these measurements for 4 - 6 different temperature values. Perform a full error analysis and compare your results with the expected values.</p>
 <h1>Questions</h1>

@@ Line 58: / Line 58: @@
-<h3>Turing on the Heater and Electron Filament.</h3>
+<h3>Turning on the Heater and Electron Filament.</h3>
 <p> Since the vapour pressure of Hg is low at room temperature (p ≈10-3 mm. of Hg) the temperature must be raised to ~160ºC to reduce the mean free path of electrons in the Hg gas. This is accomplished using the [[Media:FH_variac.jpg|Variac]]. Setting the dial to 60 should be high enough to raise the temperature of the experiment high enough. ''Be careful not to touch the experiment since the outside wall of the unit will also get very hot.'' The heating might take some time; make sure the temperature stabilized at the desired value before proceeding. Watch the thermometer to check the stability of the temperature. Once you turn on the heater, switch on the filament voltage using the switch on the power cable. This voltage level, and hence the magnitude of the electron current, can be controlled using the [[Media:FH_variableR.jpg|variable resistor]].</p>
@@ Line 70: / Line 70: @@
 <h3>Saving the Scope Traces</h3>
 <p>Using the computer to the computer to the right of apparatus.
 <ol>
 <li>Run National Instruments LabView 8.2.1.</li>
@@ Line 78: / Line 79: @@
 <li>The data is saved in the "FrankHertz Data" directory on the desktop.</li>
 <li>You can now email yourselves the data file using your email client's web interface.</li>
-</ol>
+</ol> -->
 <h2>Measurements</h2>

@@ Line 42: / Line 42: @@
 <table width=400 align=center><td>
-<p align=justify>[[File:FH_overall.jpg|500px|border|center]]
+<p align=justify>[[File:FH-exp-setup.jpg|500px|border|center]]
 <b>Figure 2b -</b> Experimental Setup.
 <br clear=right>

@@ Line 49: / Line 49: @@
 <h3>Setting up the Ramp Generator and Oscilloscope</h3>
-<p>For this experiment, we require voltage sweep from 0 to 35 V which is isolated from ground. Most function generators you find around the lab cannot give such large amplitudes, so we will need to use a power supply that will be controlled by a ramp generator.  Two power supplies (GW Instek GPS-1850D) connected in series will be controlled by a function generator (model:ASFG-2R) to generate the voltage sweep from 0 to 35 V. Note that neither output of the power supply is referenced to ground. In order to view the amplifier waveform, we will use an oscilloscope. Many oscilloscopes are designed in such a way that the outer conductor of its input jacks are automatically connected to ground. This will not work for our situation, since we need the sweep voltage to be unreferenced to ground. Therefore, we will need to operate the scope in a more advanced manner to observe the sweep. We will take the negative output of the power supply and connect it to the inner pin of CH2, and the positive output of the power supply will be attached to the inner pin of CH1 on the scope. Using the MATH function on the scope, we can display CH1-CH2, which is our sweep voltage of interest, without having connected anything to the outer conductor of the oscilloscope and forcing a ground in the circuit where one is not desired. Note, if you cannot attain a 0 - 40V ramp voltage without distortion, lower the filament voltage. </p>
+<p>For this experiment, we require voltage sweep from 0 to 35 V which is isolated from ground. Most function generators you find around the lab cannot give such large amplitudes, so we will need to use a power supply that will be controlled by a ramp generator.  Two power supplies (GW Instek GPS-1850D) connected in series will be controlled by a function generator (model:ASFG-2R) to generate the voltage sweep from 0 to 35 V. Note that neither output of the power supply is referenced to ground. In order to view the amplifier waveform, we will use an oscilloscope. Many oscilloscopes are designed in such a way that the outer conductor of its input jacks are automatically connected to ground. This will not work for our situation, since we need the sweep voltage to be unreferenced to ground. Therefore, we will need to operate the scope in a more advanced manner to observe the sweep. We will take the negative output of the power supply and connect it to the inner pin of CH2, and the positive output of the power supply will be attached to the inner pin of CH1 on the scope. Using the MATH function on the scope, we can display CH1-CH2, which is our sweep voltage of interest, without having connected anything to the outer conductor of the oscilloscope and forcing a ground in the circuit where one is not desired. Note, if you cannot attain a 0 - 35V ramp voltage without distortion, lower the ramp frequency. </p>
 <ol>
 <li> Turn on the sweep generator and select a triangle waveform.</li>

@@ Line 21: / Line 21: @@
 <li>[[Media:FH_main.jpg|Franck-Hertz Unit]]</li>
-<li>[[Media:FH_sweepgenerator.jpg|Sweep Generator]] </li>
+<li>[[Media:FH_rampgenerator.jpg|Ramp Generator]] </li>
 <li>[[Media:FH_dcamp.jpg|DC amplifier]]</li>
 <li>[[Media:FH_dcamp_powersupply.jpg|Power Supply for DC amplifier]]</li>
@@ Line 48: / Line 48: @@
 </td></table>
-<h3>Setting up the Sweep Generator and Oscilloscope</h3>
+<h3>Setting up the Ramp Generator and Oscilloscope</h3>
-<p>For this experiment, we require voltage sweep from 0 to 40 V which is isolated from ground. Most function generators you find around the lab cannot give such large amplitudes, so we will need to use a high-voltage op-amp amplifier to boost the voltage. The amplifier circuit requires +50V and -20V, which is conveniently supplied from a [[Media:FH_dcamp_powersupply.jpg|dual-output power supply]]. Note that neither output of the power supply is referenced to ground. In order to view the amplifier waveform, we will use an oscilloscope. Many oscilloscopes are designed in such a way that the outer conductor of its input jacks are automatically connected to ground. This will not work for our situation, since we need the sweep voltage to be unreferenced to ground. Therefore, we will need to operate the scope in a more advanced manner to observe the sweep. We will take the inner pin of the output from the amplifier (which contains our 0 to 40V triangle wave) and put it to the inner pin of CH2, and the outer conductor of the output of the amplifier will be attached to the inner pin of CH1 on the scope. Using the MATH function on the scope, we can display CH1-CH2, which is our sweep voltage of interest, without having connected anything to the outer conductor of the oscilloscope and forcing a ground in the circuit where one is not desired. </p>
+<p>For this experiment, we require voltage sweep from 0 to 40 V which is isolated from ground. Most function generators you find around the lab cannot give such large amplitudes, so we will need to use a high-voltage op-amp amplifier to boost the ramp voltage output from the ramp generator. The amplifier circuit requires +50V and -20V, which is conveniently supplied from a [[Media:FH_dcamp_powersupply.jpg|dual-output power supply]]. Note that neither output of the power supply is referenced to ground. In order to view the amplifier waveform, we will use an oscilloscope. Many oscilloscopes are designed in such a way that the outer conductor of its input jacks are automatically connected to ground. This will not work for our situation, since we need the sweep voltage to be unreferenced to ground. Therefore, we will need to operate the scope in a more advanced manner to observe the sweep. We will take the inner pin of the output from the amplifier (which contains our 0 to 40V triangle wave) and put it to the inner pin of CH2, and the outer conductor of the output of the amplifier will be attached to the inner pin of CH1 on the scope. Using the MATH function on the scope, we can display CH1-CH2, which is our sweep voltage of interest, without having connected anything to the outer conductor of the oscilloscope and forcing a ground in the circuit where one is not desired. Note, if you cannot attain a 0 - 40V ramp voltage without distortion, lower the filament voltage. </p>
 <ol>
 <li> Turn on the sweep generator and select a triangle waveform.</li>

@@ Line 59: / Line 59: @@
 <h3>Turing on the Heater and Electron Filament.</h3>
-<p> Since the vapour pressure of Hg is low at room temperature (p ≈10-3 mm. of Hg) the temperature must be raised to 180ºC to reduce the mean free path of electrons in the Hg gas. This is accomplished using the [[Media:FH_variac.jpg|Variac]]. Setting the dial to 60 should be high enough to raise the temperature of the experiment high enough. ''Be careful not to touch the experiment since the outside wall of the unit will also get very hot.'' The heating might take some time; make sure the temperature stabilized at the desired value before proceeding. Watch the thermometer to check the stability of the temperature. Once you turn on the heater, switch on the filament voltage using the switch on the power cable. This voltage level, and hence the magnitude of the electron current, can be controlled using the [[Media:FH_variableR.jpg|variable resistor]].</p>
+<p> Since the vapour pressure of Hg is low at room temperature (p ≈10-3 mm. of Hg) the temperature must be raised to ~160ºC to reduce the mean free path of electrons in the Hg gas. This is accomplished using the [[Media:FH_variac.jpg|Variac]]. Setting the dial to 60 should be high enough to raise the temperature of the experiment high enough. ''Be careful not to touch the experiment since the outside wall of the unit will also get very hot.'' The heating might take some time; make sure the temperature stabilized at the desired value before proceeding. Watch the thermometer to check the stability of the temperature. Once you turn on the heater, switch on the filament voltage using the switch on the power cable. This voltage level, and hence the magnitude of the electron current, can be controlled using the [[Media:FH_variableR.jpg|variable resistor]].</p>
@@ Line 67: / Line 67: @@
 <p>When the temperature is stable you can record the current-voltage characteristic of the Franck-Hertz tube. The current-voltage trace can be recorded from the connected oscilloscope after closing the (S) connection. Make sure the signal you observe does not have horizontal clipping (the peaks cut off), this can be fixed by changing the settings of the Pico-Ammeter or the potentiometer next to the 12.6 V<sub>ac</sub> transformer. (What is the meaning of the vertical cut-off?)</p>
-<p>Record an I-V curve for a lower oven temperature (between 150ºC and 165ºC). Repeat for other temperatures, so that you may comment on the effect of the Hg pressure in the tube.</p>
+<p>Record an I-V curve for a lower oven temperature (between 130ºC and 145ºC). Repeat for other temperatures, so that you may comment on the effect of the Hg pressure in the tube.</p>
 <h3>Saving the Scope Traces</h3>