Electro Technic Products Crookes Cathode Ray Tube  
Written by AnubisTTP on 2008-06-03  


"Crookes Tube" is the generic descriptor given to a wide range of hard vacuum demonstration devices, each with a different educational function. This particular tube, also known as a "beam deflection tube" was designed to illustrate how a cathode ray beam could be deflected by a magnet. A thin beam of cathode rays is projected through the slit at one end of the tube and strikes a slanted metal plate, which has been covered with a phosphor to produce a visible line discharge. When a magnet is brought near the tube, the effect of the magnetic field can be seen in the deflection of the cathode ray beam.

Though traditionally cathode ray tubes of this type were pumped down to a vacuum state, the example shown here is a newer gas filled version, most likely made during the 1950s. To make it easier to strike the tube with lower voltage supplies, this example has been filled with hydrogen, which is what produces the blue discharge at either end of the tube.


Electro Technic Products Crookes Cathode Ray Deflection Tube
Crookes cathode ray tube with power applied.

Crookes Deflection Tube
Detail of electron beam.

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