The better the vacuum, the better the electrons can travel unimpeded by collisions with gas molecules. A beam of electrons won't get far in air before being scattered.M. next said:Why do we evacuate the glass tube?
The e/m ratio, also known as the charge-to-mass ratio, is a physical constant that represents the ratio of an electron's charge to its mass. It is important because it allows us to determine the mass of the electron, which is a fundamental particle in the structure of atoms and plays a crucial role in understanding the properties of matter.
J.J. Thomson was a British physicist who is best known for his research on cathode rays and the discovery of the electron. In 1897, he conducted a series of experiments that led to the determination of the e/m ratio, which provided evidence for the existence of electrons and their charge-to-mass ratio.
Thomson's experiment involved passing a beam of cathode rays through a magnetic field and measuring the deflection of the rays. He found that the degree of deflection was directly proportional to the strength of the magnetic field and inversely proportional to the velocity of the electrons. By manipulating the magnetic field and the voltage of the cathode ray tube, Thomson was able to calculate the e/m ratio.
Thomson's discovery of the e/m ratio provided evidence for the existence of the electron and helped to establish the idea that atoms are composed of smaller, indivisible particles. This challenged the previously accepted theory of the indivisibility of atoms and paved the way for further discoveries in the field of atomic structure and particle physics.
Since Thomson's experiment, the e/m ratio has been measured and refined using various techniques, such as the Millikan oil drop experiment and modern methods like mass spectrometry. These methods have allowed for more accurate measurements of the electron's mass and charge, leading to a better understanding of the fundamental properties of matter.