Main Page/PHYS 3220/Thermionic - Revision history

Gloria at 16:44, 15 September 2020

2020-09-15T16:44:51Z

Gloria at 15:19, 18 September 2018

2018-09-18T15:19:22Z

Gloria at 14:37, 6 September 2018

2018-09-06T14:37:03Z

Gloria at 20:23, 12 October 2017

2017-10-12T20:23:20Z

Jlyons at 18:55, 12 March 2013

2013-03-12T18:55:39Z

Mgeorge at 16:24, 23 November 2012

2012-11-23T16:24:15Z

Mgeorge at 16:23, 23 November 2012

2012-11-23T16:23:09Z

Mgeorge at 16:21, 23 November 2012

2012-11-23T16:21:44Z

Mgeorge at 16:20, 23 November 2012

2012-11-23T16:20:42Z

Mgeorge at 16:19, 23 November 2012

2012-11-23T16:19:46Z

@@ Line 119: / Line 119: @@
 <p>
-The filament temperatures are to be determined from the curve given in Fig. 7 that displays the temperature-filament current characteristic for the GRD7 diode. Use the optical pyrometer to confirm the temperature. Make sure to point the securely mounted pyrometer at the glowing filament, not it’s image that is visible on the anode. Understand how this instrument works and document this in your lab write-up.
+The filament temperatures are to be determined from the curve given in Fig. 7 that displays the temperature-filament current characteristic for the GRD7 diode. Use the optical pyrometer to confirm the temperature. Make sure to point the securely mounted pyrometer at the glowing filament, not it’s image that is visible on the anode. Understand how this instrument works and document this in your lab write-up. [[Media:PyrometerManual.pdf| Pyrometer Manual]]
 </p>

@@ Line 148: / Line 148: @@
 <h2>Step 3</h2>
-<p> Carefully remove the diode assembly from the upright holder and place it on the table.  Place the given solenoid over the diode. Vary the current in the solenoid (this in turn varies the magnetic field B along the axis) to determine the cutoff field B<sub>crit</sub> for several values of the anode voltage V<sub>a</sub>. The magnetic field can be calculated from the solenoid current if one knows the number of windings per unit length (N) as B = μ I N, where μ is the permeability constant. Use the Gaussmeter to confirm your estimate of the magnetic field. Since the Hall probe of the magnetic flux meter cannot be placed at a proper angle inside the solenoid, make sure to understand how it measures a single component of the magnetic field, namely the one perpendicular to the probe. Use a cosine correction while measuring at some known angle with respect to the (hopefully) homogeneous field. Read up on how a Hall probe works and provide a brief explanation.</p>
+<p> Carefully remove the diode assembly from the upright holder and place it on the table.  Place the given solenoid over the diode. Vary the current in the solenoid (this in turn varies the magnetic field B along the axis) to determine the cutoff field B<sub>crit</sub> for several values of the anode voltage V<sub>a</sub>. The magnetic field can be calculated from the solenoid current if one knows the number of windings per unit length (N) as B = μ I N, where μ is the permeability constant. Use the Gaussmeter to confirm your estimate of the magnetic field. Read up on how a Hall probe works and provide a brief explanation.</p>
 <p>Plot B<sub>crit</sub><sup>2</sup> against V<sub>a</sub> to find the experimental relationship.</p>

@@ Line 11: / Line 11: @@
-<table width=800 align=center><tr><td>
+<table width=400 align=center><td>
 <p align=justify>[[File:Th-fig1v2.png|400px|border|center]]
 <b>Figure 1 </b>
 </p>
-</td>
+</td></table>
 <td><p align=justify>[[File:Th-fig2.png|450px|border|center]]
 <b>Figure 2</b>
 <br clear=right>
 </p>
-</td></tr> </table>
+</td></table>
 <p>From Fig. 2, note two distinct regimes of operation: a region (known as the space-charge limited region) where I<sub>a</sub> increases rapidly with V<sub>a</sub>; and the saturation region (known as the temperature limited region). At low anode voltages the cathode is surrounded by a dense space-charge of electrons, which are being continually emitted and reabsorbed. Only those electrons which are well away from the cathode are drawn towards the anode, since the electrostatic potential of the electron cloud counteracts the accelerating potential. A separate discussion of the current-voltage characteristic for this region follows below (eq. 2). As the anode voltage is increased, more electrons are drawn out of the space charge region toward the anode. For sufficiently high voltages the space-charge disappears and the beam current is limited by the rate of emission from the cathode, which leads to a saturation of the current. This saturation current depends on the temperature of the emitter and its work function, and is given by the Richardson-Dushman equation (cf.. ref. 1), </p>

@@ Line 145: / Line 145: @@
 <h2>Step 3</h2>
-<p> Place the given solenoid over the diode. Vary the current in the solenoid (this in turn varies the magnetic field B along the axis) to determine the cutoff field B<sub>crit</sub> for several values of the anode voltage V<sub>a</sub>. The magnetic field can be calculated from the solenoid current if one knows the number of windings per unit length (N) as B = μ I N, where μ is the permeability constant. Use the Gaussmeter to confirm your estimate of the magnetic field. Since the Hall probe of the magnetic flux meter cannot be placed at a proper angle inside the solenoid, make sure to understand how it measures a single component of the magnetic field, namely the one perpendicular to the probe. Use a cosine correction while measuring at some known angle with respect to the (hopefully) homogeneous field. Read up on how a Hall probe works and provide a brief explanation.</p>
+<p> Carefully remove the diode assembly from the upright holder and place it on the table.  Place the given solenoid over the diode. Vary the current in the solenoid (this in turn varies the magnetic field B along the axis) to determine the cutoff field B<sub>crit</sub> for several values of the anode voltage V<sub>a</sub>. The magnetic field can be calculated from the solenoid current if one knows the number of windings per unit length (N) as B = μ I N, where μ is the permeability constant. Use the Gaussmeter to confirm your estimate of the magnetic field. Since the Hall probe of the magnetic flux meter cannot be placed at a proper angle inside the solenoid, make sure to understand how it measures a single component of the magnetic field, namely the one perpendicular to the probe. Use a cosine correction while measuring at some known angle with respect to the (hopefully) homogeneous field. Read up on how a Hall probe works and provide a brief explanation.</p>
 <p>Plot B<sub>crit</sub><sup>2</sup> against V<sub>a</sub> to find the experimental relationship.</p>

@@ Line 12: / Line 12: @@
 <table width=800 align=center><tr><td>
-<p align=justify>[[File:Th-fig1.png|400px|border|center]]
+<p align=justify>[[File:Th-fig1v2.png|400px|border|center]]
 <b>Figure 1 </b>
 </p>

@@ Line 69: / Line 69: @@
 <table width=600 align=center><tr><td>
 <p align=justify>[[File:Th-fig3new.png|350px|border|center]]
-<b>Figure 3-</b> Trajectory of electrons in a magnetic field pointed into the page.
+<b>Figure 3-</b> Trajectory of electrons in a magnetic field pointed out of the page.
 </p>
 </td>

@@ Line 68: / Line 68: @@
 <table width=600 align=center><tr><td>
-<p align=justify>[[File:Th-fig3new.png|400px|border|center]]
+<p align=justify>[[File:Th-fig3new.png|350px|border|center]]
 <b>Figure 3-</b> Trajectory of electrons in a magnetic field.
 </p>
 </td>
-<td><p align=justify>[[File:Th-fig4.png|330px|border|center]]
+<td><p align=justify>[[File:Th-fig4.png|290px|border|center]]
 <b>Figure 4- </b>B<sub>crit</sub> corresponds to trajectory ‘d’
 <br clear=right>