LECTURE DEMONSTRATION MANUAL | Instructional Research Lab : ucla physics
Crook's Tubes

E.5.7 Crookes' Tubes

Crooks' Cathode-Ray Deflection Tube...

For showing that cathode rays are deflected by a magnetic or electric field. When a high potential is impressed across the terminals, a stream of cathode rays is established which must pass through a narrow slit in a metal plate mounted directly in front of the cathode. This narrow stream of rays traces a luminous fluorescent streak on a mineral coated screen.

Cathode rays normally travel in a straight line but are deflected through an arc when passing through a magnetic or electric field, the direction of the curvature depending on the polarity of the field with respect to the direction taken by the rays. This effect is strikingly illustrated on the screen as a magnet or current helix approaches the tube. Length about 30 cm. Including wooden stand. 

Goldstein's Canal Ray Tube ..........

For showing that there are positive rays (canal rays) as well as negative rays (cathode rays) formed by an electrical discharge in a partial vacuum. The cathode consists of an aluminum grid approximately midway in the tube. When a discharge is passed through the tube, the grid gives off high speed electrons or cathode rays which cause the lower part of the tube to fluoresce with a greenish color. The grid, being negative, also attracts positive ions which travel toward it at relatively low speed due to their great mass as compared to the mass of the electrons. Some of the positive ions strike the grid and remain, but many of them pass on through the opening into the upper part of the tube and appear as a crimson glow extending to the top of the tube. Deflection texts of the canal and cathode rays, performed by subjecting them to magnetic influence, show them to be positive and negative respectively. Diam., 4cm; height, 40cm. Including wooden base. 

Crookes' Cathode-Ray Heating Effect Tube................

For showing by the platinum heating method that cathode rays posses a large amount of  energy.

Consists of a concave cathode with a small square of platinum foil mounted at the center of its curvature. Obviously since cathode rays leave the cathode at right angles to its surface they come to a focus at a point on the platinum foild and the intensity of the energy concentrated at this point turns the platinum white hot. With a magnetic field the point of convergence may be shifted and different sections of foil heated. 

Crookes' Cathode-Ray Shadow Effect Tube .............

For showing by the shadow-method that cathode rays travel in a straight line unless acted upon by an electric of magnetic field.

Consists of a disc cathode and an anode in the shape of a Maltese cross mounted in an evacuated tube one end of which is relatively flat. When connected to an induction coil or static machine the cathode rays cause the flat end of the tube to fluoresce except for the portion shaded by the cross. By means of hinges the cross may be made to lie down or stand erect by merely tilting the tube.  When operated with the cross in a vertical position for several seconds and then with the cross lying down, the area occupied by the shadow glows more brilliantly than the surrounding area, demonstrating fatigue in a fluorescent material.

The same effect may be produced by leaving the cross erect and "bending" the rays with a magnetic field produced by a coil; or magnet.

Length about 28 cm., diameter of large end about 8 cm. Including wooden stand. 

Crookes' Cathode-Ray Mechanical Effect Tube with Rolling Wheel.....................

For showing the mechanical force excerted by impinging cathode rays. When connected to a source of high potential a stream of cathode rays passes along the upper portion of the tube. These rays impinge on the vanes of a delicate paddle wheel free to roll along glass rails between the electrodes.

Due to the kinetic energy of the cathode rays the wheel is forced to roll along the rails toward the positive electrode. Reversal of polarity obviously causes a reversal of direction of motion of both cathode stream and wheel. Fluorescent minerals on the vanes, besides enhancing the effect, serve as an indicator of the direction of the cathode stream.

Length about 31 cm., diameter, 5 cm. Including wooden stand.

Crookes' Demonstration Tube with Fluorescent Roses, 27 cm. High....

Has disc cathode directly over minerals mounted and arranged to represent two roses which under electrical excitation exhibit brilliant and colorful fluorescence. The beauty of the entire effect is greatly enhanced in a darkened room.

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