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Electromagnetism is a fundamental force of nature, encompassing all the phenomena associated with electric and magnetic fields and their interactions with charged particles. It's described by Maxwell's equations, which provide a comprehensive mathematical framework linking electricity and magnetism into one coherent theory.

In the context of cathode rays within a cathode ray tube (CRT), electromagnetism plays a crucial role. When electrons are emitted from the cathode, they move towards the anode, creating a stream of charged particles, known as cathode rays. These electrons carry an electrical charge and, according to the principles of electromagnetism, when a charged particle moves through a magnetic field, it experiences a force. This core principle is vividly demonstrated in classroom experiments where cathode rays are deflected by magnets, illustrating the electromagnetic force in action.

Cathode rays, discovered in the 19th century, are streams of electrons that can be observed in vacuum tubes. They have several distinctive properties: they travel in straight lines, they carry energy and momentum, and they can ionize gases and cause phosphorescent materials to glow. These rays possess enough kinetic energy to escape the negative electrode, or cathode, in a vacuum tube and are attracted to the positive electrode, or anode.

Interestingly, cathode rays are invisible, but their presence is detected by their physical effects, such as the fluorescence on the glass walls of the tube. It was the interaction of these rays with magnetic fields that led scientists to conclude that they consist of charged particles.

Magnetic fields exert a force on moving charged particles, an interaction is known as the Lorentz force. The direction of this force is perpendicular to both the magnetic field and the velocity of the charged particle, which means it will cause the particle to turn or curve its path without changing its speed.

The degree of deflection of particles like electrons in a cathode ray by a magnetic field can reveal important information about the particle's charge and mass. This is because the force on the charged particle is proportional to both its charge and its velocity. The larger the charge, or the faster the velocity, the greater the force and the more pronounced the deflection.

Electrons are subatomic particles with a fundamental role in chemistry, physics, and the structure of matter. They exhibit both wave-like and particle-like properties, a duality that is central to quantum mechanics. Electrons have a relatively small mass compared to protons and neutrons, which allows them to be easily affected by electromagnetic fields.

These negatively charged particles are also responsible for establishing the electrical current when they move through conductors. The study of electrons and their interactions is crucial not only in physics and chemistry but also in the practical development of electronic devices, such as the cathode ray tubes in older television and computer monitors.