J.J. Thomson's Coaxial Cylinders

In summary, the conversation discusses the setup of J.J. Thomson's Cathode Ray Experiment, which demonstrates the bending of electrons by a magnetic field. The setup includes a cathode, anode, and an electrometer surrounded by an earthed cylindrical shield. The inner cylinder serves as the electron detector and is connected to an electrometer, while the outer cylinder acts as an earthen shield. The yellow strips are connection strips and the green box is a cork. The conversation concludes with a request for how to credit the expert for their contributions.
  • #1
Christian Nguyen
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As part of an ongoing project I have been working on, I have been reading through J.J. Thomson's Cathode Ray Experiment. As part of his setup Thomson writes, "The arrangement used was as follows: — Two coaxial cylinders (fig. 1) with slits in them are placed in a bulb connected with the discharge–tube; the cathode rays from the cathode A pass into the bulb through a slit in a metal plug fitted into the neck of the tube; tins plug is connected with the anode and is put to earth. The cathode rays thus do not fall upon the cylinders unless they are deflected by a magnet. The outer cylinder is connected with the earth, the inner with the electrometer."

Could someone please explain to me the setup of this experiment, especially the part about the coaxial cylinders and how they relate to the image that he drew (I attach that with the post).

Thank You,
Christian
 

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  • #2
I am ashamed to say I had not come across this one before. The tube can demonstrate the bending of the path of electrons by a magnetic field, which would probably be applied by a pair of Helmholtz coils outside the tube.
It looks as if the cathode is A and is at Earth potential. The anode is B and is at a high positive potential relative to Earth and to A, so that electrons are drawn off the cathode at right angles to its surface. When the electrons enter the big flask, they will continue straight unless deflected somehow. The electron detector is the inner cylinder, which is connected to a (gold leaf?) electrometer. This probe is surrounded by an earthed cylindrical shield whose job is presumably to prevent the electrons being repelled by the charge accumulating on the electrometer probe. The magnetic field will cause the electrons to follow a circular path, and when increased to a critical value, will cause electrons to enter the cylinders and charge up the electroscope.
There are a number of tubes available for these sort of experiments, particularly the Perrin Tube, as you will see from the following link:
http://practicalphysics.org/types-electron-tube.html
 
  • #3
Follow Up Question: Can you help me visualize the cylinders a bit better because in the original drawing they don't look like cylinders at all.
 
  • #4
Now I look more closely, you are right. It looks as if the cylinders he mentions are the little ones with the slits, and they are connected via metal strips. These strips will still provide shielding.
I am also incorrect about the earthing of the electrodes. Thomson seems to have the cathode at a high negative potential and the anode and the plug between the two flasks are earthed. Also the electrometer shield is earthed.
 
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  • #5
Okay, thanks for all your help so far!

Let me just say it back just to make sure, I'm getting all this. The Red circle is the inner cylinder with the electroscope from a top down view. The Blue circle is the outer cylinder which acts as the earthen shield. The black lines are the slits made into the cylinders. If, that's the case, what are the two yellow strips as well as the green box? Are the yellow strips part of the outer cylinder?

Thank you for your continual help.
 

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  • #6
Christian Nguyen said:
Okay, thanks for all your help so far!

Let me just say it back just to make sure, I'm getting all this. The Red circle is the inner cylinder with the electroscope from a top down view. The Blue circle is the outer cylinder which acts as the earthen shield. The black lines are the slits made into the cylinders. If, that's the case, what are the two yellow strips as well as the green box? Are the yellow strips part of the outer cylinder?

Thank you for your continual help.
All correct. The yellow strips are connection strips. These still provide shielding. I think the green box is a cork and does nothing.
 
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  • #7
Thanks for all your help.

How should I credit you for your contributions?
 

Related to J.J. Thomson's Coaxial Cylinders

1. What is the significance of J.J. Thomson's Coaxial Cylinders in science?

J.J. Thomson's Coaxial Cylinders experiment was significant in providing evidence for the existence of electrons, helping to solidify the understanding of atomic structure and the role of electricity in matter.

2. How did J.J. Thomson's Coaxial Cylinders experiment work?

In this experiment, two charged cylinders, one inside the other, were placed in a vacuum. The inner cylinder was negatively charged, while the outer one was positively charged. The electric field between the cylinders caused particles (later identified as electrons) to move towards the positive cylinder, creating a beam of particles that could be measured and studied.

3. What were the results of J.J. Thomson's Coaxial Cylinders experiment?

The experiment showed that the particles in the beam had a negative charge and a very small mass, leading Thomson to conclude that they were subatomic particles called electrons. This discovery helped to establish the existence of atoms and the structure of the atom as a positively charged nucleus surrounded by negatively charged electrons.

4. How did J.J. Thomson's Coaxial Cylinders experiment impact the field of science?

J.J. Thomson's Coaxial Cylinders experiment was a groundbreaking discovery that greatly advanced the understanding of atomic structure and the role of electricity in matter. It also paved the way for future discoveries and experiments in the field of subatomic particles and nuclear physics.

5. Can J.J. Thomson's Coaxial Cylinders experiment be replicated today?

Yes, J.J. Thomson's Coaxial Cylinders experiment can still be replicated today using more advanced equipment and techniques. It continues to be an important experiment in the study of atomic structure and the behavior of subatomic particles.

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