The cathode ray tube, also known as the vacuum tube, contains one or more electron guns. The beams from the guns are manipulated to produce images on a glowing screen. The images may be electrical waveforms (oscilloscope), pictures (TVs, computer monitors), sonar targets, or other forms. 

Dalton’s Atomic Theory

A British schoolteacher named John Dalton came up with his theory on atoms in 1808. His discoveries were based on experiments and the laws of chemical combinations.  

Postulates of Dalton’s atomic theory are:         

1. All matter comprises indivisible particles called atoms.
2. Atoms of a similar element are the same shape and mass but diverge from the atoms of other elements.
3. Atoms can neither be developed nor destroyed.
4. Atoms of dissimilar elements may converge in a definite, simple and whole number ratio to cast compound atoms.
5. Atoms of similar elements can converge in more than one ratio to cast two or more compounds.
6. The atom is the minimal unit of matter that can take part in a chemical reaction.

Thomson’s atomic model

English physicist JJ Thomson provided one of the first atomic prototypes comprising the newly discovered particles.  

His model stated that:

• An atom approximates a sphere of positive charge and negative charge existing inside the sphere.
• The positive charge and the negative charge are comparable in magnitude. Therefore, the atom has no real charge and is electrically neutral.
• His model can be compared to a plum pudding or a watermelon. It states that positive and negative charge in an atom is randomly spread across the whole sphere, like the red portion of the watermelon (positive charge) and the black seeds (negative charge).

Thomson’s cathode ray experiment

One of the phenomenal contributions of Thomson to science is his cathode ray experiment. During the experiment, he discovered the electron, which is one of the most significant discoveries in the history of physics and chemistry. 

He was given a Nobel Prize in physics for this discovery and his research on the conduction of electricity in gases.

Apparatus for experiment

• A glass tube
• Two metal pieces as electrodes
• A unit to syphon air from the tube
• A power source to provide high voltage
• A dipole  

Cathode ray experiment procedure

• Air from the tube was removed, and high voltage was applied between the chambers containing the electrodes.
• Electricity flows from the negative part of the electrode (cathode) to the positive part (anode) through the ionised air.
• The dipoles will measure and detect the rays produced. The beam gets repelled by the negative pole and is deflected against the positive pole.
• The path of the rays can be seen by placing a phosphorescent substance at the end of the tube. The substance glows and shines when hit by the discharge ray. By observing the places where fluorescence is caused, it was noted that the deflections were towards the positive side. So the components of the discharge tube were negatively charged.

Uses of CRT

• CRTs are used as televisions.
• X-rays are produced when the cathode rays moving fast are suddenly restricted.
• The screen of a cathode ray oscilloscope and a computer monitor is covered with fluorescent components. When the cathode rays fall on it, images are created.

Conclusion

The electrons are elements found in all atoms. This hypothesis by Thomson assisted many physicists in becoming aware of an atom’s configuration for their future experiments. Thomson also identified that the cathode rays or electrons were not dependent on the equipment of electrodes or the variety or the type of gas present in the cathode ray tube.

Proton is a positively charged particle, and it takes a greater part of an atom’s volume in space. The amount of electrons scattered outside the nucleus is equal to the number of protons in the nucleus.