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Cathode Ray Tube

A Window into Electromagnetic Imaging

In Short

Classic picture tubes are based on the principle of cathode-rays (aka electron beams) which are controlled via electromagnetic fields to create a picture on a phosphorescent screen. 

When a magnet is placed in front of the screen, the electrons get deflected by the additional magnetic field, causing the electrons to hit a neighbouring pixel of the raster. By filling the screen with a fractal pattern containing large monochrome primary colour areas enhances the effect, since a slight change in the electron’s trajectory results in a strong change in colour.

Details and Theory

The CRT, a marvel of early display technology, operates on the principles of electromagnetism and precise electron manipulation.

At the heart of the CRT lies a trio of electron beams, each representing one of the primary additive colors: red, green, and blue. These beams are meticulously controlled by electromagnetic fields to scan the entire screen repeatedly. This systematic scanning, known as raster scanning, is the foundation of how images are generated on the CRT.

The CRT’s ability to produce a spectrum of colors relies on the careful coordination of these three electron beams. By modulating the intensity of each beam in response to a video signal, the screen creates a wide range of hues and shades, forming the images we see.

However, the CRT holds a secret – its sensitivity to magnetic fields. When a magnet is introduced in front of the screen, it disrupts the electron beams’ path. This interference causes the electrons to strike neighboring pixels in the raster pattern, rather than their intended targets. The result is a distortion in the displayed image, characterized by color shifts and aberrations.

Enhancing the Effect

To accentuate this magnetic distortion, the CRT screen can be filled with a fractal pattern, which contains substantial, monochrome primary color regions. This deliberate choice amplifies the impact of even slight deviations in the electrons’ trajectories. The result is a mesmerizing display where minor magnetic influences lead to significant alterations in color and image composition.

The CRT’s susceptibility to magnetic fields, when combined with its precise electron control and color modulation, creates a fascinating interplay between technology and physics. It’s a reminder of how the subtleties of electromagnetic forces can influence our perception of visual media.