In the year 1894 John Thomson carried out the research on cathode rays. He tried to estimated their velocity, which could say much about their structure. He decided to undertake this study was caused by the discovery that cathode rays could be abberate by magnetic field. If they were electromagnetic waves their aberration could be explained by granular, connected with the magnetic field structure of ether in which the waves could move. But Thomson didn't like that idea. He wanted to prove that, although these rays could stimulate glass's luminosity, they were not a kind of ultraviolet radiation as some other scientists suggested.
On the tube, in which he examined cathode rays, he marked a few points (by making scratches on the scoot covering the whole tube). Then using very fast whirling mirror, he observed the light going through the scratches. That way he measured time, in which the given points of the tube were stimulate to emit light. Thanks to that experiment he evaluated the velocity of cathode rays' motion. By the first experiment the velocity should be equal 200000 meters per second, that is 1500 times less than the speed of light; from unknown reason the result was much underrated. His experiment encourage scientists to lead on other experiments on this subject.
In the year 1895 Jean Perrin tried to evaluate the charge transported by cathode rays. He put the electric charge collector into the tube (picture no. 1). Cathode rays coming out the cathode K were falling through the whole H, placed on the anode and partly they fell on the collector F. He discovered that collector got negative charge. To confirm that the cathode rays were the ones that charged the collector using magnetic field he abberated the beam of rays in this way, that the beam reached the collector. In such situation the collector didn't get any charge. So Perrin proved that cathode rays transported the negative charge.
A year later taking into account Perrin's proof and the range of the cathode rays in the air (in standard conditions it is equal about 1 centimetre), assuming that they have molecular structure. John Thomson came to the opinion that this molecules radius should be very small; it's cross-section should be 105 times smaller than the one of air molecules. He also stated argument that, if cathode rays' features didn't depend on the kind of the gas in the tube and they consisted of particles much smaller than atoms, than that particles were parts of all atoms.
In the year 1896 he led the experiment by which he defined the connection of particles charge and its mass (q/m). He turned the cathode rays' beam on the collector. The beam transferred its charge to the collector and warmed it. He knew collector's mass, its specific heat and the heat gain. Basing on it he could evaluated thermal energy. He measured the temperature of the collector using the light thermosteam fastened to the collector. He measured the total charge gathered on the collector using very sensitive electrometer.
The total charge Q assembled on the collector one can evaluate knowing the charge of one particle q and a number of particles falling on the instrument n:
Its necessary to assume that every particle "sticks" to the collector, gives him the charge, and doesn't cause secondary emission of particles (Thomson earthen the electrode which covered the collector).
The molecule "sticking" to the collector transmits its kinetic energy E heating the collector. The energy n of molecules falling on the instrument is equal:
After dividing the formula (1) by the formula (2):
Also, the beam of cathode rays can be abberated by the magnetic field; particles move on trajectory, which is the part of the circumference of circle. So, the magnetic field has to influence with some force on molecules. Assuming that every particle has its mass m, charged q and velocity v, and that they are moving in magnetic field (which has intensity B) on trajectory with radius of curvature r we get two formulas:
the force influencing over the particle (from the formula describing magnetic component of Lorentz's force) Lorentza)
centripetal force in circle motion
Having two formulas: (3) i (7)
Thomson evaluated the velocity of cathode rays of the order of 2.4*107 meters per second; much bigger than the one he had evaluated in the year 1895; and the proportion of the charge and the mass which was between 1.0 and 1.4*1011 coulombs per kilogram.
This result was not precisely stated because of incorrect measurements; some of the assumptions were mentioned above, the other said that the whole energy had to be changed into the thermal energy of the collector and no part of that thermal energy could be transferred to the surroundings. And also, measurements of very small values; using instruments which Thomson had; had to be much inaccurate.
Thomson showed also the other way of evaluating that quantities. He joined two fields - the magnetic one and the electric one - this way that the upward magnetic force and downward electric force were acting upon the molecule.
If the electric field's intensity is equal to E, than the force acting down upon the particle charged is equal to:
If the intensity of the magnetic field is equal to B, than the upwarded force is equal to:
Equating the right sides of that two formulas; when the beam is not abberated up or down; one gets:
Up to the second method he got q/m = 0.77*1011 coulombs per kilogram. That result was much different from the first method result. The error was caused by inaccuracy in measurements.
He accepted that approximately q/m = 1*1011 coulombs per kilogram.
Thomson didn't know what are the concrete quantities of q and m. He only knew their proportion (q/m or m/q). He also knew the proportion of hydrogen's m/q, which was much bigger than the first one (the one from his experiment). So the q of electron was bigger than the q of hydrogen or the m of electron was smaller then the m of hydrogen. Taking into consideration the size of the molecule he came to the opinion that mass of the electron was the one which was very small.
The result of his experiment he published in the year 1897.
Proving of electrons' subsistence and their small size caused that Thomson formed the hypothesis that atom was divisible, and consisted of some smaller particles. He created the idea of atom as the charged ball with negative charges inside (the model of "the plum cake"). That opinion existed until 1911, when Ernest Rutheford built his own model of atom - the "planetary" one.
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