Thermionic emission is the release of electrons from a heated surface into a vacuum due to the temperature-driven increase in their energy levels.
A classic example of thermionic emission is the functioning of a vacuum tube, such as a cathode-ray tube (CRT) used in older televisions. In a CRT, a heated cathode emits electrons due to thermionic emission. These electrons are accelerated towards a positively charged anode, creating an electron beam that can be manipulated to create images on a screen coated with phosphorescent material. The phenomenon is central to the operation of vacuum tubes and other electron emission devices.
Cathode rays are streams of electrons emitted from a heated cathode in a vacuum tube, exhibiting properties of particles and electrically charged rays.
An electron gun is a device that generates and accelerates electron beams, often used in cathode-ray tubes and electron microscopes.
An electron gun serves as a reliable source of controlled electron beams due to its ability to emit and accelerate electrons. By heating a cathode, thermionic emission releases electrons into a vacuum. These emitted electrons are then accelerated by an electric field towards an anode or other electrodes, forming a focused beam. The electric field’s control allows for manipulation of the beam’s intensity and direction. This controlled electron emission has applications in displays (like CRTs), electron microscopy, and various scientific and industrial instruments.
The effects of an electric field on an electric beam are as follows:
The electric field accelerates charged particles in the beam in the direction of the field.
The beam’s trajectory changes as it experiences a force perpendicular to the electric field, leading to deflection.
Properly designed electric fields can converge or diverge the beam, focusing it to a narrow or wide cross-section.
Electric fields can be manipulated to steer the beam’s direction, allowing precise control over its path.
Varying the electric field strength can adjust the beam’s speed, impacting its travel distance over time.
Changing the electric field can modulate the energy of particles in the beam, altering their impact and behavior upon collision.
Electric fields can influence beam charging by attracting or repelling charged particles, affecting beam stability.
Deflection of electrons by a magnetic field refers to the curved path that charged electrons follow when subjected to a magnetic field perpendicular to their motion.
Electrons in a magnetic field experience a force perpendicular to their velocity, causing them to follow a curved trajectory.
When the magnetic force equals the centripetal force, electrons move in circular paths perpendicular to the magnetic field.
The direction of deflection is perpendicular to both the electron’s velocity and the magnetic field direction.
Stronger magnetic fields lead to tighter curves in the electron’s path, while weaker fields result in broader curves.
Faster electrons experience less deflection, and slower electrons experience more significant deflection for the same magnetic field.