The e/m (electron charge: mass) of electrons
Aim
The aim of this experiment was to study the movement and trajectory of an electron that moves perpendicular to a magnetic field and measure the charge-to-mass ratio of an electron.
Abstract
An electron beam was fired through a magnetic and electric field. These two fields are connected to two power supplies and these power supplies are altered. The alteration of these voltages will change the strength of the electric and magnetic fields. Varying the magnetic and electric fields will change the trajectory of the electron. From this it can be shown that the path of an electron is circular in a uniform magnetic field and parabolic in electric fields. With a known anode voltage from the electron gun and by varying the strengths of the electric and magnetic fields the charge-to-mass ratio of an electron can be calculated.
Introduction
This experiment was first done by J.J Thomson in 1897. The result from this was that he discovered that the atom was not a fundamental unit of matter and that it had charged constituents that could not be separated. Thomson investigated the nature of the cathode rays which then resulted in the conclusion that the cathode rays were negatively charged constituents of the atom; hence the discovery of the electron.
In this experiment a Thomson tube can be used to measure the deflection of electrons in magnetic and electric fields. A Thomson tube is a cathode ray tube which contains an electron gun and a florescent screen. The florescent screen illuminated when the electron gun was turned on and from this the trajectory of the electrons can be measured. By applying a known voltage for both the electric and magnetic fields the charge of the electron c...
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...result in the value for e/m being too small.
Conclusion
This experiment was to investigate the nature of a cathode ray and to investigate the ratio between the charge of an electron and its mass.
The implications of this experiment are that the electron does have a charge since its trajectory was altered in the presence of either an electric or magnetic field. It can be shown that in a uniform magnetic field the path of an electron was circular and parabolic in a uniform electric field.
Once a value for e/m was obtained the mass of an electron can be calculated using this ratio and the charge of an electing (e=1.6 x 〖10〗^(-19) C). The result from this experiment was of an order of 〖10〗^6 times too large. Subsequent errors would of have lead to this but in principle the mass of an electron can be measured if the charge of an electron is known.
Nagaoka rejected Thomson's model on the ground that opposite charges are impenetrable. He proposed an alternative model in which a positively charged center...
...the mass spectrometer. This is called an electron impact source. Gases and volatile liquid samples are allowed to leak into the ion source from a reservoir. Non-volatile solids and liquids may be introduced directly. Cations formed by the electron bombardment (red dots) are pushed away by a charged repeller plate (anions are attracted to it), and accelerated toward other electrodes, having slits through which the ions pass as a beam. Some of these ions fragment into smaller cations and neutral fragments. A perpendicular magnetic field deflects the ion beam in an arc whose radius is inversely proportional to the mass of each ion. Lighter ions are deflected more than heavier ions. By varying the strength of the magnetic field, ions of different mass can be focused progressively on a detector fixed at the end of a curved tube. Because the mass of each individual ion
7 Serway, Raymond A., Robert J. Beichner, and John W. Jewett, Jr. Physics for Scientists and Engineers. 5th ed. Philadelphia: Saunders College Publishing, 2000.
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rest mass is Me <approximately equal> 9.1 x 10 -28 g, about 1/1836 of the mass
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