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Cathode Rays

المؤلف:  Cathode Rays

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-511

2025-12-25

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Cathode Rays In considering the luminous effects of the inductive discharge we saw that the spark is longer and much more brilliant in a partial vacuum than in ordinary air. Professor William Crookes made an extensive study of the phenomena of electric discharges in high vacuum tubes. A high vacuum is one in which the gaseous pressure is not more than one millionth of that of the atmosphere. Figure 1shows the form of tube with which he studied the difference between the phenomena when high and low vacua are used. If the vacuum is low, the discharge shows a curved band of light from the cup-shaped platinum cathode to whichever wire is made the + terminal. If, however, the vacuum is high, the discharge passes from the cathode directly across the globe to the opposite wall, which glows with a yellowish green fluorescence.

FiG.1 -Crookes Tube

A study of the action of the cathode rays leads to the conclusion that they consist of a stream of minute, negatively charged particles that are projected from the cathode in a direction perpendicular to its surface, with a velocity about one tenth that of light (Fig. 1).