Electron Charge-to-mass Ratio
Electron Charge-to-mass Ratio - Related Videos
09:12
Electric Charge in a Magnetic Field
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2023
Source: Andrew Duffy, PhD, Department of Physics, Boston University, Boston, MA This experiment duplicates J.J. Thomson's famous experiment at the end of the 19th century, in which he measured the charge-to-mass ratio of the electron. In combination with Robert A. Millikan's oil-drop experiment a few years later that produced a value for the charge of the electron, the experiments enabled scientists to find, for the first time, both the mass and the charge of the electron, which are key...
03:27
Ions and Ionic Charges
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2020
In ordinary chemical reactions, the nucleus — which contains the protons and neutrons of each atom and thus identifies the element — remains unchanged. Electrons, however, can be added to atoms by transfer from other atoms, lost by transfer to other atoms, or shared with other atoms. The transfer and sharing of electrons among atoms govern the chemistry of the elements. During the formation of some compounds, atoms gain or lose electrons to form electrically charged particles called ions. When...
02:42
Formal Charges
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2020
In some cases, there are seemingly more than one valid Lewis structures for molecules and polyatomic ions. The concept of formal charges can be used to help predict the most appropriate Lewis structure when more than one reasonable structure exists. Calculating Formal Charge The formal charge of an atom in a molecule is the hypothetical charge the atom would have if the electrons in the bonds are evenly distributed between the atoms. Alternatively, formal charge results when from the number...
13:45
Introduction to Mass Spectrometry
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2023
Source: Laboratory of Dr. Khuloud Al-Jamal - King's College London Mass spectrometry is an analytical chemistry technique that enables the identification of unknown compounds within a sample, the quantification of known materials, the determination of the structure, and chemical properties of different molecules. A mass spectrometer is composed of an ionization source, an analyzer, and a detector. The process involves the ionization of chemical compounds to generate ions. When using...
03:08
Atomic Radii and Effective Nuclear Charge
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2020
The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number and distribution of electrons in their valence shells. Going across a period from left to right, a proton is added to the nucleus and an electron to the valence shell with each successive element. Going down the elements in a group, the number of electrons in the valence shell remains constant, but the principal quantum number increases by...
FAQs
Selection occurs when the electric and magnetic forces oppose one another and cancel for electrons moving at a particular speed. The beam then passes through the crossed fields without deflection, so its velocity is determined by the field strengths rather than by an uncertain initial value. This controlled speed is essential before the magnetic bending measurement begins.
After velocity selection, a magnetic field bends the beam into a measurable curved path. The magnetic force changes the electron's motion, while its mass resists that change. For a known speed and field strength, the observed curvature connects electromagnetic force with inertial resistance, allowing the charge-to-mass ratio to be inferred from the trajectory.
The electric field changes the beam's motion by accelerating the electrons, whereas the crossed-field arrangement uses electric and magnetic effects together to select speed. Once that speed is controlled, the later magnetic deflection can be interpreted under known conditions. Separating these roles makes the trajectory a usable measurement rather than an uncontrolled response.
The measurement helped establish the electron as a subatomic particle. Its significance came from linking a reproducible beam trajectory with a fundamental property of the electron, rather than relying only on qualitative observations of electrical effects. In physics, this result connected electromagnetic measurements with evidence about the structure of matter at the subatomic scale.
An experiment first applies crossed electric and magnetic fields to select a beam velocity. The selected beam then enters a magnetic field that bends it into a path whose curvature can be measured. With the electric and magnetic field strengths known, the selected speed and measured trajectory are combined to determine the electron charge-to-mass ratio.
The essential observations are the strengths of the applied electric and magnetic fields and the geometry of the beam's deflected path. The crossed-field stage supplies the velocity condition, while the later curved trajectory supplies the response at that velocity. Together, these measurements connect known electromagnetic influences to the electron's inertial response and produce e/m.
The charge-to-mass ratio remains relevant in mass spectrometry, charged-particle optics, and accelerator physics. These areas require an understanding of how charged particles respond to electric and magnetic fields. The same principle therefore provides broader scientific context for analyzing particle motion, working with charged beams, and interpreting electromagnetic behavior in research systems.