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Cathode Ray Experiment

Cathode Ray Experiment - Explanation, Diagram, Procedure and Conclusion


The cathode ray tube, which is also known as CRT, is a device that was invented in the year 1897 by Karl Ferdinand Braun. He was a German physicist who developed the device using a glass envelope or a glass tube with one end containing an electron gun that traverses within the tube. The free-moving electrons hit the fluorescent tube on the other side of the glass tube and thus cause momentary flashes which can be electrically monitored. It can be shown as an image or a picture. The picture can be later viewed as waveforms in an oscilloscope, or as pictures, detection of aircraft, and so on. The significance of this invention is that it shows the free electrons in natural colors by forming images of natural colors.

Implementing the cathode ray experiment was undertaken by J. J. Thomson. J. J. Thomson was an English physicist who began experimenting with cathode ray tubes. Because of this experiment, he could discover the existence of electrons and their properties and it was one of the major accomplishments in physics and science. The discovery led to him being awarded the Nobel prize in physics. The other properties include the charge attributed to the electron and the propagation of electric current or stream of electrons in a medium. J. J. Thomson began by taking a glass tube and attaching two metals as electrodes on the terminal ends of the glass tube. The air inside the chamber was subjected to high voltage and electric current flowing through the air medium inside the glass tube from negative terminal to positive terminal.

When J. J. Thomson designed the experiment, he ensured to subject the inside of the glass tube with a partial vacuum i.e., most of the air was drained out from within the glass tube. He then supplied high voltage between the two electrodes on the terminal ends of the glass tube. He later observed a stream of particles originating from the negative electrode, which was also called a cathode, to the positive terminal or the positive electrode also called an anode. Since the ray originated on the cathode terminal, it was named cathode ray. For this explanation, it is preferred to call the stream of particles a cathode ray. The stream of particles were essentially electrons that migrated from the cathode to the anode and thus electric current was induced in the partial air medium inside the glass tube. This led to the discovery of electrons which changed the course of the discipline of physics.

Besides this discovery, the experiment could describe the characteristic properties of its inherent ability to be attracted to positive charges or protons or holes. They also explained the magnitude of charge it holds along with the mass ratio. The experiment was set up by utilizing a glass tube with two electrodes in the terminals of the glass tube; the air was removed and the pressure inside the glass tube was thus reduced.

Procedure of the Cathode Ray Experiment

  • The apparatus is arranged such a way that the terminals have high voltage with the internal pressure reduced by removing the air inside the tube
  • High voltage in the terminal results in ionization of partial air inside and thus gas becomes the conductor
  • Electric current propagates as a closed-loop circuit
  • A dipole was set up to recognize and measure the ray produced
  • Due to the dipole, the cathode rays began deflecting and repelled from the dipole and moved towards the anode
  • phosphorescent substance was placed such that the rays hit the substance, causing small sparks of light, which detects the stream of rays

Cathode Ray Experiment

After this procedure was followed, a few conclusions were drawn by J. J. Thomson. The rays that were seen moving from cation to anion were negative in nature. This then aided future physicists to understand the modern structure of an atom. They also found out that the natural, physical, behavioral properties of electrons do not get altered or changed by the amount of voltage, type of gases, and its constituent ratios. This ensured that the electron is an independent subatomic particle that has its characteristics and behaviors which was later classified by the future set of physicists.

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