[THIS POST IS NOW IN ITERATIVE MODE PLEASE WAIT FOR MORE SHORTLY]
COURSE CODE: 4BPH4C1
CORE COURSE VIII – ATOMIC AND NUCLEAR PHYSICS
Unit I POSITIVE RAYS
Photo electricity: Photoelectric emission – laws – Lenard’s experiment – Richardson and Compton experiment – Einstein’s photo electric equation – experimental verification of Einstein’s photo electric equation by Millikan’s experiment – Photoelectric cells.
POSITIVE RAYS
- A Historical Exposition of Positive Rays from Cambridge University with beautiful and very explanatory animations.
- A Wikipedia article on Anode Rays
- Click to download "Rays of positive electricity, and their application to chemical analyses" by J.J.Thomson, Master and Originator of the Subject. This file is in DJVU format, which has many advantages over PDF. Main advantage is it is light weight and does not consume RAM space. To view this file type, please download WinDjView program(only 2.8 MB file size) for Windows platform here. Android users just search for a suitable App in the Google Play Store of which there are plenty.
- Click to download J.J.Thomson's Paper on positive rays
 |
Anode ray tube showing the rays passing through the perforated cathode and causing the pink glow above it |
By Kkmurray - Own work, CC BY-SA 3.0,
https://commons.wikimedia.org/w/index.php?curid=14960885
What are Positive Rays?
Properties of Positive Rays
What are Positive Rays?
When a high voltage (~10000 volt) is applied between anode and perforated cathode of a gas discharge tube maintained at high vacuum (~0.001 mm of Hg), faint luminous rays are seen to extent from the back of the cathode. These rays are experimentally shown to possess positive charge. These rays are called positive rays.
1. Positive rays consist of positively charged particles.
2. The nature of these rays depends on the gas used in the discharge tube.
3. These rays travel in straight lines. They cast a shadow of the object in their path.
4. These rays get deflected by an electrical field, and bend towards the negative plate. Thus the deflection of the positive rays is in a direction opposite to that shown by the cathode rays.
5. These rays are also deflected by the magnetic fields in the direction opposite to that of the cathode rays.
6. These rays can produce mechanical as well as chemical effects.
7. The ratio of charge (e) to mass (m), i.e.,(e/m) for the particles in the positive rays is not the same for all gases.
8. The ratio e / m for the positive rays is very low as compared to the e / m value for cathode rays.
9. Positive rays affect photographic plate.
10. They can produce ionization in gases.
11. They cause fluorescence.
Specific Charge (or) Charge to Mass Ratio (e/m) of Positive Rays
Charge to Mass ratio of a charged particle serves much like a signature of that particular species of that particle. Charge and Mass along with Spin constitute key characteristics of molecular, atomic and sub-atomic particle species. If we neglect relativistic effects, which we can always do with greater confidence in discharge tube experiments, charge to mass ratio alias specific charge becomes the single most important characteristic of charged particle species determining their behavior under the action of electromagnetic field.
For Cathode e/m ratio is a constant immaterial of the gas used inside the discharge tube. This is because cathode rays consist of electrons emitted from negative electrodes, which has a fixed charge to mass ratio. On the other hand positive rays consist of gas ions and hence their charge to mass ratio depends on the gases used to fill the discharge tube. Positive rays have thousands of times less specific charge than the cathode rays.
What is a Spectrum ?
spectrum (n.) 1610s, "apparition, specter," from Latin spectrum (plural spectra) "an appearance, image, apparition, specter," from specere "to look at, view" . Meaning "visible band showing the successive colors, formed from a beam of light passed through a prism" first recorded 1670s. Figurative sense of "entire range (of something)" is from 1936.
Credit:http://www.etymonline.com
So, A spectrum is an entire range of color,charges,masses,speeds or something.
Mass Spectrum is sorting ions with respect to their masses or more particularly their Mass to Charge ratio or Charge to Mass ratio(works just as fine).
Aston's Mass Spectrograph
Francis William Aston (1 September 1877 – 20 November 1945)
- Aston won the 1922 Nobel Prize in Chemistry for his prominent work in Physics(!!?). Click Here to Download and Read Aston's Nobel Lecture.
- For Historical Details Please Visit Here.
- Click Here to read a Nice Paper on Development of Mass Spectrometers.
- Download a History Poster Here.
Aston Working With His Mass Spectrometer - Can You See the Large Electromagnet?
Bainbridges's Mass Spectrograph
1. Positive rays consist of positively charged particles.
2. The nature of these rays depends on the gas used in the discharge tube.
3. These rays travel in straight lines. They cast a shadow of the object in their path.
4. These rays get deflected by an electrical field, and bend towards the negative plate. Thus the deflection of the positive rays is in a direction opposite to that shown by the cathode rays.
5. These rays are also deflected by the magnetic fields in the direction opposite to that of the cathode rays.
6. These rays can produce mechanical as well as chemical effects.
7. The ratio of charge (e) to mass (m), i.e.,(e/m) for the particles in the positive rays is not the same for all gases.
8. The ratio e / m for the positive rays is very low as compared to the e / m value for cathode rays.
9. Positive rays affect photographic plate.
10. They can produce ionization in gases.
11. They cause fluorescence.
Specific Charge (or) Charge to Mass Ratio (e/m) of Positive Rays
For Cathode e/m ratio is a constant immaterial of the gas used inside the discharge tube. This is because cathode rays consist of electrons emitted from negative electrodes, which has a fixed charge to mass ratio. On the other hand positive rays consist of gas ions and hence their charge to mass ratio depends on the gases used to fill the discharge tube. Positive rays have thousands of times less specific charge than the cathode rays.
What is a Spectrum ?
Credit:http://www.etymonline.com
So, A spectrum is an entire range of color,charges,masses,speeds or something.
Mass Spectrum is sorting ions with respect to their masses or more particularly their Mass to Charge ratio or Charge to Mass ratio(works just as fine).
Aston's Mass Spectrograph
 |
| Francis William Aston (1 September 1877 – 20 November 1945) |
- Aston won the 1922 Nobel Prize in Chemistry for his prominent work in Physics(!!?). Click Here to Download and Read Aston's Nobel Lecture.
- For Historical Details Please Visit Here.
- Click Here to read a Nice Paper on Development of Mass Spectrometers.
- Download a History Poster Here.
 |
| Aston Working With His Mass Spectrometer - Can You See the Large Electromagnet? |
Bainbridges's Mass Spectrograph