Canal Ray Experiment

Dhristi JEE 2022-24

What are Canal Rays?

A Canal ray (also known as a positive or anode ray) is described as a positive ions' beam, created by certain gas-discharge tube types. These rays were observed in 1886 in Crookes tubes when the German scientist named "Eugen Goldstein performed experiments." 


Later on, anode rays work by the scientist Wilhelm Wien and J. J. Thomson led to the mass spectrometry development. So, it is said that Dempster is the one who discovered canal rays. He was also one of the first spectrometers to use such ions’ sources.


Canal Ray Experiment

The canal rays experiment is the one that led to the discovery of the proton. The proton discovery has happened after the electron discovery has further strengthened the structure of the atom. In this experiment, Goldstein happened to apply a high voltage across a discharge tube that had a perforated cathode. Also, a faint luminous ray was seen extending from the holes of the back of the cathode.


Apparatus of the Experiment

The apparatus of this experiment includes the same cathode-ray experiment, made up of a glass tube containing two metal ion pieces at different ends that acts as an electrode. These two metal pieces are further connected with an external voltage. The air evacuation lowers the pressure of the gas present inside the tube.


The Procedure of the Experiment

Let us discuss more details about the procedure of the experiment, as listed below.

  • As the apparatus is set up by evacuating the air and giving a high voltage source for maintaining a low pressure inside the tube.

  • The high voltage is passed to the two metal pieces to ionize the air by making it an electricity conductor.

  • Thereby, the electricity starts to flow as the circuit is complete.

  • When the voltage was increased to thousands of volts, a faint luminous ray was seen, extending from the holes present behind the cathode.

  • These rays moved in the opposite direction facing the cathode rays and were called canal rays.


Explanation

When a higher voltage is applied, the experiment ionizes the gas, and it is the positive ions of gas that constitute the canal ray. It is the kernel or nucleus of the gas that is used in the tube, and thus, it has different properties to that of the cathode rays, made up of electrons.


Differences between Cathode and Anode Rays

Basically, in the first Canal ray experiment, William used the Crookes tube supplying high voltage and gradually reduced the pressure within the tube chamber from 0.01 to 0.001 atm. Also, he noticed a certain beam of light starting to emanate from the tube's cathode, and this travelled throughout the tube upon reducing the pressure further.


Then, the light emitted from the ray was passed via the strong electric field formed between two plates, charge positive and negative. The light beam was found to curve towards the positive plate and was thus charged negatively. It was named Cathode Rays because it originated from the Cathode of the Tube.


After that, using a perforated Cathode (Cathode with fine pores), he conducted another experiment. Even this time, too, he saw the light, but now, starting from the middle of the tube. Upon increasing the voltage and reducing further pressure, the beam went towards the cathode. The beam bent towards the negative plate when the light beam was placed in between an electric field, and hence, these rays were charged positively.


But we cannot call them Anode Rays since they weren't emitted from the AnodeAnode. Therefore, they were known as Canal Rays because they formed light 'canals' when they left the cathode's perforations.


Production of Anode Rays

When a high range of voltage is applied to the tube, the electric field accelerates the small ions count (electrically charged atoms) that are always present in the gas, created by natural processes like radioactivity. These collide with the gas atoms by knocking the electrons off of them and creating added positive ions. These electrons and ions strike more atoms, in turn, creating added positive ions in a chain reaction. Then, all the positive ions get attracted to the negative cathode, and a few of them pass through the holes in the cathode if any. These are known as the anode rays.


Conclusion

  • Unlike the cathode rays, canal rays will depend upon the nature of gas that is present in the tube. This is due to the canal rays being composed of positive ionized ions formed by the ionization of gas present in the tube.

  • The charge to the ratio of mass for the ray particles was different for different gases.

  • The particle's behavior in the magnetic and electric fields was opposite compared to the cathode rays.

  • Besides, a few particles that are charged positively carry multiples of the fundamental value of the charge.

  • E. Goldstein also concluded that apart from the cathode rays that pass from the negatively charged electrode to the positively charged electrode, there is another set of rays that move exactly in opposite directions which is from a positively charged electrode to a negatively charged electrode and these rays are canal or anode rays. They were further analyzed and it led to the discovery of a positively charged subatomic particle called “Proton”. 

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FAQs (Frequently Asked Questions)

1. What is meant by the Goldstein experiment?

E. Goldstein was the person who conducted an experiment in which he passed electricity through two electrodes that were placed on either side of the glass or vacuum chamber. Then the electrodes were connected to an external electricity source. When the electricity was passed through the electrodes, the positively charged ions were emitted from the positive electrode and these rays were known as the canal rays. Goldstein conducted discharge tube experiments on his own in the 1870s named Kathodenstrahlen, or the cathode rays, which are light emissions, examined by others. He found a few major properties of the cathode ray, which led to their subsequent discovery as the electron, which is the first subatomic particle. Finally, he concluded that in addition to the cathode rays or ions that travel from the negatively charged electrode towards the positively charged electrodes, other rays travelled in opposite directions which is from the positively charged electrode to the negatively charged electrode. These rays deflected oppositely when they were subjected to magnetic and electric fields.

2. Why are the anode rays referred to as canal rays?

The anode rays are the particle beams that travel in the opposite direction to the "cathode rays," the electron waves, which move through the Anode. These positive rays were referred to as Kanal Strahlen, by Goldstein, "canal rays" or "channel rays," because the channels or holes in the cathode formed them. Canal rays have positively charged ions that move from a positive electrode towards a negative electrode in a glass chamber through a gas. They deflect in an opposite direction that cathode rays deflect when both of them are subjected to magnetic and electric fields. By further analyzing these rays, positively charged subatomic particles also known as protons were discovered. Canal rays, also known as anode rays, travel in a straight line but have lesser velocity than the cathode rays and can penetrate through thin metal plates. 

3. Describe some differences between canal and cathode rays?

Canal rays are also known as anode rays, they are positively charged ions that travel through a gas chamber to reach the negatively charged electrode. These rays were discovered by E. Goldstein when he was conducting an experiment and further analysis of these rays has led to the discovery of positively charged protons. On the other hand, cathode rays are negatively charged electrons that travel from the negatively charged electrode to the positively charged electrode. Both the rays deflect in opposite directions when they are brought under the effect of the magnetic and electric fields. Cathode rays travel in straight lines, thus they cast a sharp image or reflection. Unlike the anode rays, the properties of the cathode rays are not dependent on the gas present in the vacuum tube. Phosphorus is an element that glows when the cathode rays fall on it. Similar to the anode rays, cathode rays also penetrate through thin metal plates. These rays are lighter than the lightest element that is hydrogen. J.J Thomson discovered a subatomic particle related to the cathode rays in 1897, they are  known as “electrons”


Cathode rays are negatively charged, whereas the Canal Rays are positively charged. 

  • Cathode rays emanate from the cathode but the canal rays do not emanate from the Anode, and they are produced inside the chamber by the gas molecule's collision. 

  • Cathode rays are drawn to positive electrodes in an electric field.

4. Explain the Production of Canal Rays.

Canal rays also known as the anode rays were discovered by E. Goldstein when he was experimenting. These rays are positively charged ions that pass through a chamber of gas to reach the negative electrode also known as a cathode. The apparatus required to produce the canal rays is a glass tube having two metal ion pieces on either side and further connected to an external circuit.  The metal piece acts as an electrode. The air is evacuated to reduce the pressure on the gas, the electricity is passed through the electrodes and in this process, the gas gets ionized. 


Electrons, which are emitted from the cathode, collide with the gas atoms present in the tube by knocking either one or two additional electrons out of each atom. These collisions leave behind ions that are charged positively. The positive ions that are produced travel towards the cathode. And, any of the positive ions pass via perforations that create canal rays in the cathode disc. Both magnetic and electric fields deflect the channel rays in a similar direction to the cathode rays.

5. What are the characteristics of canal or anode rays?

Canal rays also known as the anode rays were discovered by E. Goldstein when he was experimenting. They are positively charged rays that move towards the negative electrode also known as a cathode in a discharge tube when high voltage electricity is passed through the tube. Following are the applications of canal or anode rays:

  • They are positively charged ions that move in an enclosed place along with the gas.

  • They are oppositely deflected to the deflecting direction of cathode rays due to magnetic and electric fields. 

  • They travel at a lower velocity compared to the cathode rays and travel unidirectionally.

  • Anode rays affect the photographic rays and also produce fluorescence and ionize the gas through which they pass. Positively charged protons are discovered after analyzing the anode rays. 

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