Katodisäteen

Katodisäteen, or cathode rays, are streams of electrons emitted from the negative electrode (the cathode) in a vacuum tube when a sufficiently high voltage is applied. The rays travel from the cathode toward the anode and can be observed when they strike a phosphor-coated screen, causing fluorescence. They are produced regardless of the gas present in the tube, provided the vacuum is sufficient and the electrode is heated or otherwise energized.

Historically, cathode rays were studied in discharge tubes in the late 19th century. William Crookes conducted early experiments with vacuum tubes, and in 1897 J. J. Thomson showed that the rays could be deflected by electric and magnetic fields in a way that depended on their charge-to-mass ratio. From these measurements he concluded that cathode rays are negatively charged particles—electrons—that are constituents of atoms.

Properties and behavior of cathode rays include their emission from the cathode, their tendency to travel in straight lines in the absence of fields, and their deflection in electric and magnetic fields, which reveals information about the particles’ charge-to-mass ratio. When they strike materials, they can produce fluorescence and, at higher energies, X-rays.

Applications and significance: cathode rays underpinned the development of cathode ray tubes used in old television sets, computer monitors, and oscilloscopes. They also led to the discovery of the electron and the establishment of key concepts in atomic physics. Modern devices rely on electron beams in electron microscopes and other instruments, while CRT technology has largely been replaced by flat-panel displays.