Canal Ray Experiment

Canal Ray Experiment

Canal Ray experiment is the experiment performed by German scientist Eugen Goldsteinin 1886 that led to the discovery of the proton. The discovery of proton which happened after the discovery of the electron further strengthened the structure of the atom. In the experiment, Goldstein applied high voltage across a discharge tube which had a perforated cathode. A faint luminous ray was seen extending from the holes in the back of the cathode.

Canal Ray Experiment

Apparatus of the experiment

The apparatus of the experiment incorporates the same apparatus as of cathode ray experiment which is made up of a tube made of glass containing two pieces of metals ions at the different end which acts as an electrode. The two metal pieces are connected with an external voltage. The pressure of the gas inside the tube is lowered by evacuating the air.

Procedure of the experiment

  • Apparatus as set up by providing a high voltage source and evacuating the air to maintain low pressure inside the tube.
  • High voltage is passed to the two metal pieces to ionize the air and make it a conductor of electricity.
  • The electricity starts flowing as the circuit was complete.
  • When the voltage was increased to several thousand volts, a faint luminous ray was seen extending from the holes in the back of the cathode.
  • These rays were moving in the opposite direction of cathode rays and were named canal rays.


When very high voltage is applied, it ionizes the gas and it is positive ions of gas that constitutes the canal ray. It is actually the nucleus or kernel of the gas that was used in the tube and hence it has properties different from the cathode rays which were made up of electrons.


  • Unlike cathode rays, canal rays depend upon the nature of gas present in the tube. It is because the canal rays are composed of positive ionized ions formed by ionization of gas present in the tube.
  • The charge to mass ratio for the particles of the ray was found to be different for different gases.
  • The behaviour of particles in an electric and magnetic field was opposite to that of cathode rays.
  • Some positively charged particles carry multiples of the fundamental value of the charge.

Frequently Asked Questions – FAQs

Who discovered the canal rays?

Dempster was one of the first spectrometers to use such sources of ions. He never succeeded in using magnetic bending. By the light they released while travelling through gases and by the fluorescent patch they created on the discharge tube wall, Goldstein had discovered canal rays.

Why anode rays are called canal rays?

These rays are particle beams that travel in a direction opposite to the “cathode rays,” which are electron waves that move through the anode. These positive rays were called Kanal strahlen by Goldstein, “channel rays” or “canal rays,” because the holes or channels in the cathode formed them.

What was Goldstein experiment?

In the 1870s, Goldstein conducted his own discharge tube experiments and named Kathodenstrahlen, or cathode rays, the light emissions examined by others. He found some major cathode ray properties, which led to their subsequent discovery as the electron, the first subatomic particle.

What is the difference between cathode rays and canal rays?

Cathode rays are charged negatively, while Canal Rays are charged positively. Cathode rays emanate from the cathode, while the rays of the canal do not emanate from the anode, but are produced inside the chamber by the collision of gas molecules. In an electric field, cathode rays are drawn to positive electrodes.

How canal rays are produced?

The electrons emitted from the cathode collide with the gas atoms found in the tube, knocking one or two additional electrons out of each of these atoms. This collisions leave behind ions which are positively charged. The produced positive ions travel towards the cathode. Any of the positive ions pass through the perforations that create canal rays in the cathode disc. Both electric and magnetic fields deflect the channel rays in the same direction from the cathode rays.

For more information about canal ray experiment, the discovery of proton or other sub-atomic particles, download BYJU’S – The learning app to play store and app store.

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