. Conduction of electricity through gases and radio-activity; a text-book with experiments . ionization chambershown in Fig. 37. Adjust the distance between the plates Pand P to about 2 cm. Adjust the width of the cone of raysso that they do not touch the plates as they pass through thegas. Exhaust the vessel to a pressure of about 1 mm. Con-nect 5 and S to the electrometer and to the negative pole ofa battery respectively in the usual way. Apply a potential ofonly a few volts to S and measure the current between theplates when the rays are acting. Increase the potential by a few volts and mea
. Conduction of electricity through gases and radio-activity; a text-book with experiments . ionization chambershown in Fig. 37. Adjust the distance between the plates Pand P to about 2 cm. Adjust the width of the cone of raysso that they do not touch the plates as they pass through thegas. Exhaust the vessel to a pressure of about 1 mm. Con-nect 5 and S to the electrometer and to the negative pole ofa battery respectively in the usual way. Apply a potential ofonly a few volts to S and measure the current between theplates when the rays are acting. Increase the potential by a few volts and measure thecurrent. Continue this untila potential of about 300 voltsis reached, keeping the pres-sure constant. Plot the curvefor current and voltage. Re-peat this for two or threedifferent pressures below amillimeter and plot the curves obtained shouldpresent the general formshown in Fig. 43. It will beobserved that for compara-tively low voltages the firstpart of the curve up to a point A is of the same form as thesaturation curve at atmospheric pressure, but when the voltage. IONS BY COLLISION IO5 is increased beyond a certain amount the current begins toincrease again, at first slowly and then very rapidly. Thevoltage at which this increase begins will depend upon thepressure of the gas. The increase of the current beyond thepoint A must be caused by an increase in the number of ionsdue to some cause other than the original ionizing source, forwe have already seen that Rontgen rays produce fewer ionsat low pressures than at high pressures. Now we know that if a stream of rapidly moving cathoderay particles or electrons be allowed to pass between two elec-trodes in a cathode ray tube an ionization current is producedbetween the electrodes, showing that the rapidly moving elec-trons or ions must have ionized the molecules of the ionize a molecule a certain definite amount of energy isrequired. A moving ion possesses kinetic energy, and if thevelocity is suffic
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