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Crookes Tube Schematic (hot cathode variation)
The low voltage power supply (A) is connected to heat the cathode (C). The higher voltage power supply (B) energizes the phosphor-coated anode (P). The mask (M) is connected to the cathode potential and its image is seen on the phosphor as a non-glowing area. This tube may be built without supply A by using a cold cathode
The Crookes tube is an evacuated glass cone with 3 node elements (one anode and two cathodes). It is an invention of the 19th century scientist William Crookes and is an evolutionary development of the earlier Geissler tube.
The low voltage power supply (A) is connected to heat the cathode (C). The higher voltage power supply (B) energizes the phosphor-coated anode (P). The mask (M) is connected to the cathode potential and its image is seen on the phosphor as a non-glowing area. This tube may be built without supply A by using a cold cathode
The Crookes tube was designed to explore phosphorescent effects observed in the Geissler tubes — at high vacuum any phosphorescent material within the low pressure envelope would glow, but only at one terminal. The excitation of the phosphor was attributed by Crookes to what he called cathode rays, and which are now interpreted to be particles rather than rays; these particles are electrons.
At the small end of a glass cone, an electrically heated wire, called the cathode, produces electrons. At the opposite end, a phosphor coated screen forming an anode is connected to the positive terminal of a voltage source of modest voltage (a few hundred volts), whose negative end is connected to the cathode. In between the cathode and the anode is placed a third element, a flat plate with some distinctive shape (the shadow mask), also connected to the cathode. When the appropriate voltages are applied to the various elements the screen will be seen to glow. A non-glowing image of the shadow mask will be imposed upon the screen.
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